Having done boxing/jiu jitsu/wrestling for a few years I can tell you bodybuilders would have an extremely hard time. As the Gracies showed technique is more important than size, and bodybuilders don’t practice striking or grappling. A UFC guy grappled with an NFL lineman a couple of weeks ago, big weight difference, the football player said he was interested in MMA so they rolled pretty casually. The lineman, an athlete not a bodybuilder, tapped out 4 times in a couple of minutes.
MMA is also an anaerobic sport. So the 40 min slow cardio I’ve seen some bodybuilders advocate would do absolutely nothing. They’ld gas after a minute and it would be a lot easier to choke that neck like a tree trunk, or just pound their face to a bloody pulp. There are no muscles that help prevent knockouts, as most are due to a rotation of the head/jaw or a shot to the tip of the jaw in which the force travels to the brain, not the neck.