The answer is yes, wasn't it stated that the slayer and vampire's were created from the same source/demon. A shadow demon or something. The only difference is that he lacks the prophetic dreams , but then again most slayers do...actually no, he had some gift of prophecy when Darla came to visit him in a dream. So yes he is a slayer, a slayer is just a living vampire who doesn't require blood, and they seem to get stronger faster too.
From time to time like in "Graduation Day Part II", everyone is capable of becoming a slayer of some form. Also in the opening of Season 6, the remaining scoobies became slayers albeit without the benefit of slayer strength or recovery powers. Someone raised in Quor'toth would be likely to be much more physically fit than the scoobies but that does not make him a slayer. As the progeny of two vampires, he is the sole example in a category all its own.