I don't think it can be Matt because it would be inconsistent with his sexual identity crisis over Jean Grey -- the Carver had already raped his first man by that point. I suppose you could create a scenario where Matt as the Carver thinks that the rapes aren't really about his desires, but it seems very odd.

Also, I'm confused why the Carver would leave a semen-filled condom at the kill site if "he" doesn't want anyone else getting credit for his crimes. Unless Kit actually planted it or unless he just planned to punish Christian for a short time, I can't make sense of the idea.