I've never seen the Draco-as-werewolf theory before. I've seen Snape-as-vampire, of course - I've even read fanfic with that as a theme. That comes not only from all the things you said above, but because right after Snape assigned "werewolves" to the Gryffindor third years, Lupin assigned "vampires" and it does seem rather quid pro quo.