To tell you the truth, I don't think he'd want to. Angelus wasn't like Spike. He could fight when he had to, sure, and we saw that he was damn good at it, but for him it was never about the thrill of battle or the challenge of it all. He was a pretty sadistic guy, and they always showed that he heavily targeted his victims. He tortured and tormented them. He was cunning in a sick and twisted sort of way, but he never really showed any inclination to fight if he didn't have to, unlike Spike. So I think he would have steered clear of any Slayers that might have crossed his path.