I wonder why it is necessary (or useful) to imagine that there is an original, drawn from real life, standing behind Kinbote, Shade, etc. Seeking out VN's allusions and sources is often a very rewarding exercise, as these allusions directly relate to interpretation. But I have yet to see a case where any of VN's major characters can be productively (from the reader's perspective) linked to an actual person. The closest we come is Galya Diment's unearthing of Pnin's relationship to Szeftel, but even that revelation, though solid enough, is less interesting than VN's own relationship to Szeftel--that is, knowing that Szeftel is behind Pnin advances our understanding of the novel only marginally, if at all. Positing Ginsberg as Kinbote's original can only reduce the compexity of VN's character, and I might argue the same for those looking for Shade's poetic progenitor, though I am eager to read Sam Gwynn's essay.
I am currently enjoying Eric Naiman's Nabokov, Perversely, though he too can't resist constructing VN's characters from his own imagination. In an (unnecessary) attempt to improve the argument for a bawdy reading of VN, Naiman argues that "Quilty is probably [such certainty!] a composite, combining two wide-ranging giants of successive generations: [Shakesperean scholar] Quiller-Couch and Nabokov's friend Edmund Wilson." Of course it might be so, but the degree of mind-reading necessary to assert, with confidence, this theory is unavailable to most of us. In any case, the exercise is counterproductive, as it turns Quilty into a stitched together version of someone(s), rather than an original in his own right.