OK, I'm man enough to admit when I'm wrong. Jam Master Jay was not in fact a rapper (despite reports of a performance at a Boca Raton restaurant). I'll have to file this under "learned something new today". I was never a big rap fan, but loved Run DMC back in the day. Grand Master Flash, Whodini, Beasties, Cypress Hill and a Tribe Called Quest all made it onto my playlist in my life at some point too. I wanted a Run DMC guy. And while I don't see why the distinction was necessarily worthy of note, I do now admit that a DJ in a rap group is not by association a rapper. My bad.
That said, I'm going to change my pick to Q-Tip from A Tribe Called Quest. Lord have mercy, I have seen the light.
http://www.youtube.com/watch?v=zeiiee10VFY