By the same token, MMAers may want to compete in San Shou to test their stand up skill, as well as their take down and wrestling skills. I can tell you this, in my state MMA is not legal so many of the local gyms compete in whatever combat sport is legal here and go out of state for MMA. This could be the case for someone competing from MMA or other things.
I'm sure there have been MMA guys who also competed in boxing, kickboxing, or Muay Thai, not really a stretch that they would compete in San Shou.
"The hero and the coward both feel the same thing, but the hero projects his fear onto his opponent while the coward runs. 'Fear'. It's the same thing, but it's what you do with it that matters". -Cus D'Amato