^^Yes, the slashings started before he came. In fact, we were first introduced to Quentin Costa as the "brilliant facial reconstruction surgeon" who repaired Sean's face after the Carver slashed him.
My theory: Costa had worn out his welcome in Atlanta, and was most likely close to being fired for being a drug-addled psychopath. I believe he created the Carver persona not only to give outlet to his growing rage, but also to "drum up business" as it were. Being the pre-eminent facial reconstruction surgeon, he naturally figured it was only a matter of time before someone called him in to perform. Bam! Instant celebrity. When McNamara/Troy started fixing the Carver's victims pro bono, Costa became enraged, and did the one thing he knew would get him called in: attacked Sean. Brilliant.
Kit, I'm surprised a seasoned detective like yourself couldn't figure this out. But I'll let you slide, given the fact that you are approximately as hot as two suns going supernova. (Supernovae?)