Honestly a back story isn't entirely necessary. Once we've got the gist of the lore surrounding the creatures, we become the back story. 

The actions of our characters create a history to go by. If the wolves don't have an outstanding role in this universe thus far besides being a nuisance to humanity and Vampires alike, so be it. Our characters can initiate a change.

On the wolves: I think that because the wolves are able to go between quadrupedal and bipedal stances, they'd be sorta faster.  I get what you mean about their size being a factor so I suppose they may not be as nimble as the vampires. 

Remember, wolves have always been the Vampires nemesis because they were the only organisms that could rival (and kill) vampires. So that could be the underlying reason for vamps to want wolves eradicated.

As for external indicators for wolves, why not make their eyes glow in the dark, as well?