I believe that BJJ is key to success in the world of MMA but BJJ is not the only martial art out there so that being said what other martial arts are necessary to be successful in MMA.
Muay Thai Kickboxing - Everyone needs some sort of stand up game
Wrestling - A little more brute force than bjj but the wrestling take downs are my opinion the most effective especially with gloves on (very gross motor skills).
Other than that I am not sure what I would say is a recipe for success.