No, we don't know it, because he never did it. But its a hypothetical question with no real answer, so believe what you will I guess.
Maybe Vasili Oschepkov, co-founder of SAMBO and taught both Judo and Karate, and for the Record I believe Kaerlin has at least some training, as Judo/Sambo were requirements for all Soviet boys in schooling, but he may have already been fully dedicated in a wrestling school by then, so maybe not.
Karelin would have been a monster......one of the strongest humans in history, a machine. I could just dream of seeing Karelin Karelin lifting that big doofus Tim Sylvia over his head and smashing him into the mat! muhahahaha.......i would most enjoy that.