RZA: Piano The Knux: multiple instruments (they were marching band geeks :P) Mos Def: Bass Tyler the creator: Piano Wyclef Jean: Guitar Flavor flav: Bass and Piano
Rap is music. A lot of mainstream rap is just rehashed sex, drugs and how rich they are. That sort of stuff is fine,it's part of rap culture. It's just way too milked as a cash cow.
Gangster rap is pretty scary though. There used to be positive messages, but then you have rappers like bobby shmurda who rap purely about gangster activity without any real message.