When this question was originally asked I briefly discussed it with the querent in comments. At that time I was quick to point out that if one were looking for religious references that Pan might be nearer the mark, and that searching the terms 'god', 'pan' and 'balloons' brings up references to this poem, and that Pan is associated with a flute or pipes and the devil isn't, and that he fact that Pan is associated with Spring and fertility, which the devil isn't. Boys and girls called from their childish playtimes by a goat-footed character playing a whistle sounded, to me, more like sexual awakening than children being stolen away by Satan.
Now I think that all of that can be true, and OP's view can be true Just as well, but only so far as these would be allusions Cummings understood he was invoking.
The poem has its genesis in a real childhood memory of Cummings'
First sketched as an exercise for a class at Harvard at a time (about 1914) when free verse excited undergraduates but was discouraged by professors, the poem captured the poet's childhood memories of a street that flooded in spring each year—at the same time that a balloon-seller began showing up, blowing his whistle.
For me this means that we can regard the original memory as a palimpsest , with the bare bones of a real incident overwritten with invitations to the reader, who does not share that memory, to view the recollection in a more universal light.
The balloon seller's whistle literally tempted the children away from their present pursuits, casting them aside to race after the new and the bright, and the queer, old, lame seller with his deformed foot, who might have been spurned by children in other circumstances is himself covered by the glamour cast by the spring and by the bright, taut balloons.
Parental imprecations to be wary of strange men, and he surely cuts a strange figure, are rendered void by the promise of balloons in the wet, bright spring sun.
Cummings draws attention to important things in his poems with the use of capitals, so I read the introduction of the capital M in the second occurrence of 'balloonman' as significant, it emphasises that the balloonman is a man and not, after all, either Pan or the Devil, despite the fact that his description invites us to consider those entities.
In essence what the Devil/Satan/Pan and even Satyrs all represent, in one way or another, is temptation, that which steals human attention from it's course and has us act on our impulses, without judgement. So the balloonman is a man who embodies temptation through what he has to offer, rather than through his own person and so, like those other entities can be read either as one of those personification of temptation who exert a malign force on us, or merely as a man who offers us something we want.
Considering in relation to this reading @KittenWithAWhip's point made in comments that 'we know e. e. cummings was a very strong Christian', I don't think this means we should exclude the possibility of his making reference to entities not strictly within that mythology.
i thank You God for most this amazing
day: for the leaping greenly spirits of trees
and a blue true dream of sky; and for everything
which is natural which is infinite which is yes
From "i thank You God for most this amazing" (1950)
It would not be counted an orthodox christian belief that trees have spirits, and we must also remember that [in Just-] was written when cummings was in his twenties, and his views them may not have been the views of his later life. Bear in mind also that Cummings' family were Unitarian, rather than more mainstream christian. Wikipedia states that Unitarians:
believe that Jesus Christ was inspired by God in his moral teachings and that he is the saviour of humankind, but he is not comparable or equal to God himself. Which sets it at significant odds with more mainstream Christian doctrines,