I think (although I could be wrong) that Severus addressing Remus as "Wolf" either affectionately or insultingly is fanon only. A lot of writers do use it- I lnow I do, and I suspect I picked it up first from geri_chan and then from snapelike (and others too.)
I just skimmed through all the dialogue from the books either between Severus and Remus or involving them (there is surprisingly little) and nowhere does Severus call Remus "wolf". (You can read all the JKR Snape dialogue at the Canon-Snape site - the link is on the sidebar at snapedom.)
But I just got a note from one of my betas on one of my stories, that says Severus usually calls him "Werewolf" in human form, but "Wolf" in animal form. I don't actually undrstand what your beta means here - I certainly couldn't find any evidence of at Canonsnapesite. He refers to him as the werewof, for example in POA when he says "I’ll drag the werewolf. Perhaps the dementors will have a kiss for him too __" and "Don’t ask me to fathom the way a werewolf’s mind works."
Is Gryffindorj on your flist? Gryffindorj will know. Anyone who knows that the word Centaur isn't capitalized in canon off the top of her head, is practically a canon-bible!