Krav Maga's emphasis on real-world self-defense and potentially lethal techniques makes it less suitable for the regulated environment of MMA competition.
Joe Rogan never fought in the UFC. He's been a commentator for the UFC for close to 20 years now. Rogan was a competitive Tae Kwon Do fighter in his late teens-early 20's and very successful. He's also an avid Brazilian Jiu Jitsu practitioner for years now, but I don't know his Belt level.