Does anyone bring in extra bodies for training camps? I know top guys get together and work with each other, but do they bring in guys like boxers do to spar with?
I remember seeing that GSP brought in Stephen "Wonderboy" Thompson several camps back strictly as a sparring partner. I think Stephen was about 50-0 in kickboxing at the time.
Dan Henderson also brought in Cyrille Diabate prior to the Anderson Silva fight largely because of his muay thai and similar frame to Silva.
Happens often I imagine, especially if they're looking to combat a certain body type or style.
Well i'm a chubby heavyweight lol. The chance to train with great fighters will only make me better going forward. It would be worth the butt kicking I would take.
I'm a nobody and I do that for my fights. Its just smart training. 
Yeah i do that locally too. I meant more like big camps bringing in partners for their top fighters.
I think they try and get guys to mimic the style. There was a vid of Overeem training with a real big guy that I imagine was to prep him if he faced Semmy in the GP. I know Cain brought in a real big wrestler that Brock has actually faced in College.