I've checked, it appears 'Direwolf' is not a vanilla nickname.
Anyway, aside from its inappropriateness in this game, why do you object to the word as such, if I may ask?
Oh thank gods for that.
My distaste is a bit difficult to pin down, but it has something to do with using a prehistoric animal as a prop in a game about (largely) historical or at least nearly-historical epochs. It relies too much on the inherent cool factor in a name like direwolf - which in itself is a bit of an awkward calque on the Latin Canis dirus.