It's a sprung matted floor, just like the octagon is. It's designed to dissipate some of the impact/shock from falling, but not as much as a trampoline (which takes nearly all of it).
Anybody who denies that Professional Wrestling is not a physical and/or athletic profession is nuts. That said, Brock is not doing 300 matches a year like the lower tiered and smaller show guys; he does maybe 1-2 real matches a year. And while I'm sure he still trains the rest of the year and that such training has some conditioning effect on his body; there is still a big difference between such conditioning and fighting.
As the great Sugar Ray Robinson used to say, "it's the shot you don't see coming that really hurts/drops you." Even though some of the impacts in Pro Wrestling are huge, they always know when and where they are coming and as such can mentally and physically prepare themselves to take them. You can take a ton more impact and not go down if you know it's coming. That is the biggest difference between the two types of impact/conditioning. That and the fact that strikes in fighting are specifically placed and designed to damage your body, while the impacts in Pro Wrestling are designed to minimize them.
As far as Lesnar being able to take Hunt's best shots, I strongly disagree. Hunt walk off KO'd Roy Nelson, who has otherwise proven to have Homer Simpson syndrome. Hunt is a former K-1 champion and save for Alistair Overeem (who TKO'd Brock with a liver kick, something that I could see Hunt also doing with a liver lunch) is the best striker that he has faced to date. Velasquez dropped Lesnar, it's ridiculous to suggest that Hunt could not.
That said, I completely agree that Lesnar could also potentially take Hunt down and smother him/submit/TKO him on the ground for 5 rounds. We shall see.