WWE wrestlers that have a background in Martial Arts (Sheldon Benjamen/Wrestling, CM Punk/Ju Jitsu, Brock Lesnar/Wrestling) would have/had/or would have had a fair chance in MMA.
But WWE guys like John Cena, Kane, and The Undertaker would've had much MUCH harder time transitioning into MMA because they don't have any type of Martial Arts background. They have nothing to build off of. This is why I have a hard time believe that Batista would be able to compete effectively without several years of traing. He would have to start from scratch.