All forms of professional fighting have rules that were put in place to help fighters stay alive and ready for their next fight, and the only cheats you could ever sneak by would be small scale stuff.
Crafty fighters come up with all kinds of (mostly gross) ways to give them an edge in the ring, and since mixed martial arts bouts usually involve some sort of grappling MMA fighters often use their stink to give them a leg up.
But stink isn't as effective as hard training, and MMA fighters train so hard they risk being knocked unconscious or receiving a career ending injury just to make sure they're in top shape when they enter the Octagon.
Read Stink Is A Weapon: 5 Facts About MMA Fighting (Not Seen On TV) here (contains NSFW language)