"Could somebody explain San Shou to me?"
Sure. In a nutshell it's similar to the standup portion of MMA. you can kick, punch, shoot for takedowns clinch and throw. In the format called sanda, you're allowed to throw knees as well. One thing that makes it different is that you only get about 3-5 seconds in the clinch to attempt a throw or takedown etc before the ref stops it, so the clinch and throwing is pretty fast paced. once someone hits the ground the ref breaks the action.
I love Matt Hughes.. but there is no way he'd beat Cung in San Shou. Cung is one of the best in the world at his weight class.
Neither he nor Karo have the striking and they both come from a grappling world that gives them the ability to get a dominant position or grip and work at it.. they would get pretty frustrated by the ref stopping them just as they started to get into their comfort zone.