Although it made for some wildassed comedy, it's been confirmed by one of the writers behind the show that the Eminem/Bruno stunt on Sunday's MTV awards was staged.
Scott Aukerman, the head writer for the show confirmed on his blog that the Eminem Bruno stunt was scripted. Scott says:
"Yes, the Eminem-Bruno incident was staged. They rehearsed it at dress [rehearsal] and yes, it went as far as it did on the live show"
Here's the Eminem Bruno Stunt Video