what you have to do really depends on the person you are recording. would you de-ess 50 cent? if you did, you'd take away his signature "i'm from NY but i sound southern" sound.
many of the rappers and dancehall artist i deal with get so use to shouting into the mic live that they think they have to do the same thing in the studio, which causes me to have to rolloff some of the lowend with EQ.
whether you use reverb, just like an R&B tune, really depends on the tempo and vibe of the song. if its a rap love song [Biggie "im fucking you tonight"] there's noticable reverb on his vocals (as well as the lead vocalist), whereas Biggie's "10 crack commandments" has plenty of vocal doubling but i don't perceive any reverb.
my biggest problem with rappers in the studio is consistency in vocal volume delivery. just like an inconsistent bass player, you end up putting a compressor on the vocals or (my preference for rap vocals) doing some wave editing to bring the low phrases up.