MMA is all about ground and pound?
BJ Penn (former UFC LW Champ), his last few fights were stand up wars, even if they ended in submission, there was little GnP. He was then defeated in a stand up battle.
GSP, while very GnP centric, uses his striking to get the fight there.
Anderson Silva is ALL stand up and has, in fact, some of the best Muay Thai in MMA, possibly some of the best Muay Thai in the world but I'm not qualified to make that Judgement.
Shogun Rua is a stand-up fighter. Fight with Coleman was a stand up war, ending in Coleman's demise. Fight with Liddel was all standing, ending in a KO. First fight with Machida was 25 minutes of stand-up. Second fight was two rounds of stand up, ending in a KO.
Brock Lesnar is the only champion who is, IMO, based on GnP.