There is indeed a resonance with Norse mythology. In Völuspá, stanza 39 according to Codex Regius, or 24 according to Hauksbók (there are otherwise only variations of tense between them in this stanza), we are told of a giantess in an eastern forest, giving birth to a brood of wolves:
The giantess old
in Ironwood sat,
In the east, and bore
the brood of Fenrir;
Among these one
in monster's guise
Was soon to steal
the sun from the sky.
Völuspa, translated by Henry Adams Bellow
The mother of Fenrir is called Angrboða in Hyndluljóð. The sun is said by Snorri to be chased by the wolf Sköll, who will catch up to it and devour it at Ragnarök. (Sköll is sometimes conflated with Fenrir in other poems).
As to if and how this resonance is important, it is more difficult to say without access to The Fall of Arthur, but it could range from the entirely coincidental ("wolf in forest" and "east" are not so specific so as to make it totally improbable), via subconscious influence and general allusion to a specific reference.
My guess is that Tolkien did have the Völuspá in mind, but that he used it mostly for the effect of the imagery, and perhaps for the suggestion of world-shattering events (in the Codex Regius, the stanza comes right before the events of Ragnarök, in Hauksbók, it comes before the Aesir-Vanir war).
There could be a further suggestion of The Battle of Maldon as well, where the Viking host invading form the east are called "slaughter-wolves".
