Sumo is virtually entirely about trips, throws and balance, no? All crucial skills for MMA.
Yes thats right
I just watched some Sumo vids on youtube, many are from the big belts those guys wear without the use of legs. But many are also from leg sweeps, not precisely how Lyoto does them but I guess he took them over from it and from his other Martial arts. Probably a combination of everthing!