There's not much progressive rock with rapped vocals. One definite is Candiria, a prog-metal/math punk/jazz fusion group.
WhoSampled lists loads of rappers that sample prog.
Haven't came across a band that sounds like 70s prog with rapped vocals.
I keep hearing "prog hip-hop" used in the media but by that they usually mean alternative/underground hip-hop.
I think the idea of doing a progressive rock band with rapped vocals has potential to be huge. I mean, there were two major artists that started off as rappers then started doing country/blues music mixed with rock, maybe there should be a major progressive rock/hip-hop crossover.