Do rappers sing raps or say raps?
- sing, because raps are songs.
- say, because you don't really sing a rap, you say it.
Both are possible, but sing seems preferable. You could also say do rap and perform rap. Rappers rap raps too.
: to perform rap music
However, when looking through instances of say rap, it was hard to find one that matched the meaning we seek. Many examples were in the sense of speaking about rap, not performing rap. For example "How do you say rap in X language?" It was easier to find say a rap, as in
Say a rap, [homeboy], get the mic out your butt
in "Pimp the Hoe" by Too Short. Examples of sing a rap were much easier to find.
So all in all, I would say that, between sing and say, sing is preferable.