Well, way back with the first induction in 1986 you had plenty of artists who were getting in not as rock artists themselves but as people who have influenced the rock genre. Jimmie Rodgers, James Brown, Robert Johnson, they don't play rock music. But they influenced the genre enough to warrant induction. The same case could easily be made for Tupac. Rap music has been closely intertwined with rock music for a whopping 30 years now. Tupac, as one of the most influential rap artists, has also had a tremendous influence on rock music.
Anyhoo, me, I'm just glad that Yes finally got in. The hall's refusal to acknowledge quintessential subgenres of rock is my biggest gripe with them.