Yes I'm pretty sure they do. Maybe not all, but definitely most (most of the ones I've seen anyways!)
Here's the most memorable example of the smallest dicked bodybuilder I ever saw: I went with my boyfriend to his brother's bodybuilding competition. We were backstage helping him to prepare, and then went into the mens room to pee. While there, a huge muscled Asian guy came running in. He obviously needed to take a leak really bad and was barely able to hold it in. Finally a urinal opened up and we let the Asian bodybuilder go first. Before he even got to the urinal, he whipped his dick out of his pants in front of everyone, then walked up to take a piss! My boyfriend and I got a good eyeful of the guy's manhood. It was really small. We both giggled accidentally, but he didn't seem to notice.
Then we each got the urinals on either side of him and we both just stared down at his tiny nob and jelly-bean sized testicles and tried not to laugh too loudly, but we did! He noticed that! He kept looking back and forth at us both and then down at his almost not-existing penis. Then my boyfriend said to me something like, "I guess it's true what they say about bodybuilders!", then made a pinching gesture with his thumb and forefinger, indicating smallness, and nodded at me but in the direction of the Asian bodybuilder!
At first, the guy just grimaced, gave an uncomfortable chuckle and looked up at the ceiling. But then he got pissed and asked us why we were looking at his dick and called us "faggots" and said he would kick our asses!
My boyfriend and I hurried up and got the hell outta there! We tried to avoid him for the rest of the night. We didn't mean to be assholes or anything, we were just having a little innocent fun.
He was the only bodybuilder I ever saw in person. And like I said, his dick was really small! I've seen plenty of nude bodybuilders in porn, and most of them are about average-sized. So generally, yes I would have to say bodybuilder do have small dicks. | 
