Discussions of the topic contain sensitive content.
No, his biographers don’t think there’s good evidence.
The closest seems to be Andrew Field’s VN, the life and art of Vladimir Nabokov (1986):
Uncle Ruka has been well described in Speak, Memory, but the whole
story has not been told: Uncle Ruka was in love with his nephew
Vladimir and used to cause awkwardness in the family by trying to
fondle him too much in public when he was a little boy.
The source for this happens to be Field’s notebook in which he made notes during interviews with Nabokov, his family and friends. Even here, the author doesn’t suppose abuse and states that “Nabokov later regretted that he had not visited his uncle more often”.
Andrew Field has a history of personal relationships with Nabokov who agreed to supply materials for his biography – but later they fell out. His research was criticized by reviewers and Nabokov’s family: e.g. James Wood in The Guardian calls it “inaccurate and hubristic”, and more sympathetic LRB review says “Field is rather fond of filling blank spaces with daring speculations”. This is probably not the best source.
The definitive biography of Nabokov was written by Brian Boyd, one of the leading Nabokov scholars. The first volume, Vladimir Nabokov: The Russian Years (1990), describes the episode thus:
Vasily, however, sporting a violet carnation, would stay behind in the
sunny dining room, and sit young Vladimir on his knee, fondling him
"with crooning sounds and fancy endearments, and I felt embarrassed
for my uncle by the presence of the servants and relieved when my
father called him from the veranda: 'Basile, on vous attend.'"
Humbert's first feignedly nonchalant fumbles with Lolita, a painter's
penchant for little Ada's bottom, the adult Nabokov's disapproval of
homosexuals and his solicitude for childhood innocence may all have
their origins here.
Boyd doesn’t say there’s evidence that any abuse did happen, and merely speculates on the sources of literary inspiration.
Comparisons with Lolita are not convincing. Boyd describes Nabokov being good at sports (boxing, football, tennis) and his happy childhood:
Nothing sustained Nabokov as a writer more than his memories of a
radiantly secure childhood that let him grow up an exceptionally
assured young man.
Compare it with the famous tennis passage from Lolita. She plays well, but never wins because something went wrong:
yet I insist that had not something within her been broken by me - not
that I realized it then! - she would have had on the top of her
perfect form the will to win, and would have become a real girl
champion.
Andrea Pitzer in The Secret History of Vladimir Nabokov (2013) doesn’t think we can know what precisely happened:
Elena Nabokov’s brother, Uncle Ruka, adored the young Volodya and made
much of him. Nabokov remembered for decades the attention paid to him
by his uncle, who took him on his knee and, with special names and
sweet words, fondled him. Fondle is Nabokov’s word, and his account of
their interactions was so nuanced as to leave events entirely unclear,
while still striking an insistent note of unease.
As odd as his uncle was, Nabokov would long be troubled by the
condescension Ruka endured even from those who liked him. As if in
response, Nabokov would later build character after unsettling
character who is mocked and misunderstood but who has his own secret
life in tow.
Some journalists were more direct. Lev Grossman in the essay The gay Nabokov on “uncle Ruka”:
He appears to have subjected Nabokov to a mild form of sexual abuse
But Grossman hasn’t conducted novel research and relies only on Boyd’s biography and Nabokov’s account in "Speak, Memory", already cited in the question. So this probably doesn’t deserve much attention.
Lastly, this was discussed on Reddit. User JBOBHK135 suggested that “indeed Vladimir was abused by his uncle”. When asked for evidence, JBOBHK135 replied that “no it’s not an official fact”, but there are “rumours and allusions” in Nabokov’s books, and “it’s more about putting all the pieces of the puzzle together”.
There’s simply no solid factual evidence. Therefore, until someone shows how the abuse claim can be inferred from piecing together Nabokov’s allusions, there‘s nothing to discuss.
American scholar Brandon Centerwall did exactly this kind of work (or so he said).
Hiding in plain sight.
he claimed to have known as many as six pedophiles - a surprising
number. I have no doubt I have met as many pedophiles as Nabokov, but
not a single one to know of.
…muses Brandon S. Centerwall in his essay Hiding in Plain Sight: Nabokov and Pedophilia (Texas Studies in Literature and Language, Vol. 32, No. 3, Artistic Tensions: Tradition, Society, Memory, and Gender (FALL 1990), pp. 468-484).
In the first part of the essay, he establishes that Nabokov was a closet pedophile. His exact reasons are beyond the scope of this answer. Then he moves to the origins of this trait.
Centerwall is very suspicious about Nabokov’s butterfly collecting hobby:
He spent hundreds, thousands of hours probing their sexual organs (for
that was his specialty) - a singularly appropriate occupation for a
closet pedophile. Since his appetite for impaling butterflies began
about age seven, it is there we must look for the roots of his
pedophilia.
So what are they? Centerwall is refreshingly straightforward:
As fate would have it, young Vladimir had a pedophile for an uncle.
Called "the butt-grabber" by the peasants on his estate, Vasiliy
Rukavishnikov ("Uncle Ruka") was a flamer of the old school, indelibly
described by Nabokov in his autobiography, Speak, Memory: "...mincing
feet in high-heeled white shoes"
Centerwall used Field’s 1986 book with its “uncle in love” storyline. Now, the inheritance problem:
Vladimir's parents apparently did nothing effective to protect him
from Uncle Ruka's advances, perhaps because Ruka was a childless
millionaire who might well make their son his heir. Some things can be
overlooked, if the stakes are high enough
Uncle Ruka did make Vladimir his sole heir, and young Nabokov
inherited the Ruka millions in 1916, after his uncle died […] Perhaps
it was payment for services rendered.
Boyd says the latter claim is incorrect, relying on his research in the archives:
Although the homosexual Uncle Vasily had been intensely fond of his
handsome nephew, the inheritance of the family property had long been
settled, as a matter of family order rather than personal favor, when
the first three children were born: Rozhdestveno would go to Vladimir,
the St. Petersburg home to Sergey, and Vyra to Olga. V. D. Nabokov was
very much against his son inheriting such wealth at such an early age.
Some numerological similarities with Lolita:
When young Vladimir was age twelve, his uncle Ruka was thirty-seven
years old. By seeming coincidence, Humbert is also age thirty- seven
at the time he begins sexually abusing his twelve-year-old step-
daughter. There are other similarities. Like Humbert, Uncle Ruka was
of independent means, charming, not conspicuously employed in gainful
activities, a sometime poet, and a cosmopolitan European with a taste
for French and French affectations; Uncle Ruka died of a chronic heart
condition at age forty-two, as does Humbert.
(E-copy of Speak, Memory I used says the uncle died aged 45, Russian Wiki gives 44 and a half – and 27 years for the age difference)
The author takes Lolita as a riddle, and since a riddle can’t mention its answer, a lot of attention is paid to what is not there:
So strewn is Lolita with thematic red herrings that it takes an effort
to realize that the answer to the riddle is contained within the two
words the author never, never uses: pedophilia and molestation
What else is missing?
There is an odd lacuna in Humbert's narrative […] There is one act,
though, he does not describe - fellatio. When it comes to this quite
ordinary sexual act, Humbert's pen dries up.
And now, in a rather long passage, Centerwall delivers the meat of his argument:
There is one scene in Lolita where Humbert describes fellatio
implicitly, as a visual image. Following his first night with the
twelve-year-old Dolores Haze, he paints in his imagination an erotic
mural. One scene in the mural is "a choking snake sheathing whole the
flayed trunk of a shoat" (136). The picture equates the child molester
with a pig, his young victim with a choking snake. The pig metaphor
requires no elaboration. The choking snake, however, is odd on two
counts. First, there is no reference in the text to Lolita choking,
either then or later. Second, a snake in all its phallicness is not a
logical metaphor for a young girl, whereas it would be appropriate for
a young boy. The image points outside of the text to another part of
Nabokov's mental landscape - to a scene where a young boy is choking
as he is coerced (gently, of course) into sucking the phallus of his
pig-uncle. With such a burden of hidden humiliation, it is no wonder
Nabokov killed butterflies the rest of his life; it is no wonder he
yearned to exorcise magically his secret shame by making another child
endure what he had suffer.
How was all this received? Bruce Stone in Nabokov’s Exoneration: The Genesis and Genius of Lolita labelled it “a masterpiece of stupidity”. Elen Pifer (Nabokov and His Fiction: New Perspectives) says “Centerwall, whose conflation of author and narrator leads him to declare in no uncertain terms that Nabokov was ‘a closet pedophile’”. On the other hand, Krin Gabbard (online journal PsyArt, The Circulation of Sado-Masochistic Desire in the Lolita Texts) states that
Centerwall “has persuasively argued” his case. Centerwall’s essay is also in “Further Reading” section of the book Vladimir Nabokov in context. So some people are impressed by his scholarship.
In 1992, the author published a more ambitious sequel (Vladimir Nabokov: A case study in pedophilia, Psychoanalysis & Contemporary Thought), in which “[Nabokov’s] pedophilia was, it is argued, further rooted in his grandfather having married his lover's daughter”. Unfortunately, this article is paywalled.
Solving Nabokov’s Lolita Riddle
Dear D Barton Johnson
Please visit my website www.lolitariddle.com. I
have just published a code-cracking book in Australia which proves
that Nabokov wrote Lolita as a semi-autobiographical account of his
own terrible sexual abuse as a boy at the hands of his molesting,
pedophilic Uncle Ruka. Nabokov invented an ingenious code which hinged
on a deliberate 'Freudian slip' (what he called 'blunders'). There are
several errors in his memoirs and his translation of Pushkin's Eugene
Onegin - especially in the stanza referring to trysts with uncles and
children by the old lime trees.
From The Nabokovian
In interviews, Nabokov used to compare writing a book with creating a riddle. Joanne Morgan in Solving Nabokov's Lolita Riddle took this puzzle-solving approach. Working on social problems of pedophilia, she became interested in Nabokov. University presses rejected her book (maybe being too conservative for her methods), so she decided to self-publish. I don’t have access to the book. I’ll rely on a review text and some archived entries from her site.
Morgan agrees with Centerwall that Nabokov was both a pedophile and victim of abuse. Her methods to prove this are highly inventive. To give an example, she conducts an analysis of the famous chess problem that “was incorporated by Nabokov into Chapter Fourteen of his autobiography”. There's an encoded message.
In the stunning 1940 chess problem Nabokov composed, White has been
set the task of achieving check-mate in two moves. As the chess
diagram at Figure 2 below illustrates, two pawns in this game face
immanent danger of being 'queened.' The White Pawn on b7 is one square
away from reaching the end of the board, whereas the Black Pawn on c3
is two squares away from his 'coronation.' If the Black Pawn advances
from c2 to c1, we can expect it will be molested by the
incestuously-minded Black Knight that stands, poised and at the ready,
nearby.
For White it is always tempting to advance the White Pawn to b8 where
it would normally be exchanged for a queen. Within his memoirs,
however, Nabokov idiosyncratically instructed that the pawn should be
exchanged for a knight. (This may be Nabokov-speak for how a queened
pawn, or sexually abused boy, is in danger of developing a pedophilic
orientation as an adult.) In any case, whether it is exchanged for a
knight or a queen, advancing the White Pawn to b8 (a ruse that is the
equivalent of the 'irresistible try') is the wrong move to make. White
cannot ensure check-mate in the prescribed two moves if it 'queens'
the pawn on b8. This is because Black can then move the Black Pawn on
square d7 to d6, thus placing the White King under check from the
Black Rook on g7.
Provided that we follow Nabokov's instructions and exchange the pawn
for a knight, the author then insisted that the best move open to
Black was to avoid placing the White King under check from the Black
Rook. Instead he advised that the Black Pawn on c3 should be advanced
to square c2. This move, I strongly suspect, is the equivalent of the
"modest dilatory move" (Speak Memory, 230). Via this ingenious code
Nabokov managed to divulge how Uncle Ruka escalated his abuse from
fondling to anal digital penetration. (Ruka richly deserved his
reputation as a 'bottom-feeler.') The Black Pawn is now only one move
away from his fraught rendezvous with the Black Knight on square c1
and no chess piece can intercede to prevent its perilous advance.
Non-traumatic anal penetration can be very pleasurable for children
(as well as adults). It is clear that this indelicate maneuver,
performed by Ruka upon Vladimir, placed his nephew in grave and
immediate danger.
How was it received? The book drew the ire of then-23-year-old Sarah Holland-Batt. In her review, she reminds us that Nabokov disliked “criticism reliant upon derivative symbolism”, and therefore it’s unlikely that he encoded images in his novels to symbolize sexual abuse. So she doesn’t see any Freudian possibility here:
Nabokov never — explicitly or implicitly — hinted that his uncle
behaved with impropriety (indeed, to the contrary, in Speak, Memory,
Nabokov recalls rescuing with alacrity an inherited cane of Ruka’s
from beneath the wheels of a train
Furthermore
Ruka is mentioned on a total of fourteen of the some 256 pages of
Speak, Memory, and Nabokov recalls a ‘sense of security, of
well-being, of summer warmth’ (62) attached to his memories of his
uncle, so Morgan resorts to a conflation of the author and his
fictional characters in order to make her case.
The book didn’t convince Holland-Batt:
By approaching the text with her paedophilic bent, while aiming to
uncover the ‘true’ answer to a riddle, Morgan has (coincidentally and
conveniently) identified a riddle revolving around paedophilia.
Morgan’s work is also riddled with factual inaccuracies: for instance,
Humbert Humbert, the French protagonist of the novel, miraculously
becomes ‘Swiss’ (19); Humbert’s first love, Annabel Leigh, transforms
into the eerie twin of Poe’s ‘Annabel Lee’ (19), and Quilty’s peculiar
handwriting becomes Humbert’s (50), to name but a few. Morgan’s
superficial knowledge of Nabokov’s work is manifest throughout the
text: she asserts that ‘Lolita was one of very few pieces of prose by
Nabokov where he adopted the first person narrative’
To be strictly accurate, Morgan’s scholarship is more reminiscent of
Charles Kinbote’s — Nabokov’s comically deranged commentator in Pale
Fire — sans the incidental chuckles which ensue as a result of
Kinbote’s hilarious misreadings.
Ultimately, Morgan’s fare is severely wanting in terms of its mode of
expression, methodology, and its scholarly integrity.
Full text of the review is available here. For Morgan’s reply, see here.
Here’s Dmitri Nabokov’s comment.