Brock is still a freak of nature, but he definately used steroids IMO. I remember a old interview with Bautista (who also probably used) where he talks about Brock's freakish strength, in Dave's words "Brock could rip my arms off" or something like that.

There are definately MMA fighters that use, with no out of competition testing, why wouldn't you? Especially in the UFC, where some guys can actually afford it.