Sometimes, werewolves are aliens too. :3
But, if fishes aren't always Water, and Crocodiles can be ground, I'm sure a werewolf can be a Fairy. Though I hope not, I can't see a werewolf Pokémon being done that well. D:
Maybe a Little Red Riding Hood-style wolf wearing old-woman clothes? Would tap into the entire "fairy-tale" aspect of the Fairy type.