Teddy Riley isn't categorized as a rap producer because he was a member of two huge R&B groups. Many don't associate him with Kool Moe Dee, Wrexx N Effect, or Dougie Fresh like they do Tim w/ Jay and Missy. Timbaland was helming quite a few Hip Hop albums and breaking Hip Hop acts. I'm not sure if Teddy ever fully produced or even helmed a Hip Hop album in the way he did Guy, Blackstreet, and MJ's Dangerous.
Teddy should get much more props than he does as a Hip Hop producer though. Without him, there's no Tim or Neptunes or even a Devante and many other producers. He is one of the producers in Urban music that laid the ground work for "super producer".