Ghost_Dogg,
yep, he's definitely done some roids. Even if he had the best possible genetics you could imagine, he still wouldn't have been able to build that bod (or maintain it, if he had already built it earlier) in prison without some anabolic assistance. For a couple of reasons: first, prison food is shit, and as far as I'm aware, this gentleman was pennyless during his incarceration. Which leads me to believe he couldn't by any stretch of the imagination have been able to bring in the neccessary legal supplements from the outside, not being able to afford it, even if it was possible (which I doubt: I think they have a strict policy on what types of food items can be brought in from the outside). Second, prison life isn't exactly the best environment to build massive muscles: sure, it's the stereotype, but a false one at that. Most 'big' prison dudes are just fat and tattooed to look menacing and manly. Besides, I hear they have restrictions as to what kind of training equipment they can have in maximum security pens. I doubt Kimbo would have been able to build such a well rounded physique with the limited equipment available.
Furthermore, even if he had built himself up before getting locked up, he surely would have lost a lot of his muscles and gained some fat during his stay. Prison life can be very stressful, which leaves cortisol running rampant in the inmates' veins (cortisol being the primary muscle breakdown hormone, which is released during times of distress or anguish), which would be yet another reason why I find it hard to believe he could have built/maintained such an excellent bod without hormonal manipulation.
Real prison life isn't exactly the OZ- you don't see guys of Chucky Pancamo's caliber walking the hallways all that often, unless they're resourceful guys who have managed to smuggle in steroids.