This is a sad story for the UFC really. I'm all for people trying to tick things off their bucket list, but using the UFC makes the company look like a joke. If he wanted to compete in MMA that badly, go sign up for a fight or two in some local circuit, do all the training, and be satisfied you tested yourself. Coming into the biggest MMA organisation for a fight? Yeah, it destroys a lot of the work the UFC has done to try and turn itself into a legitimate sport. It's different if you pull in pro fighters from other disciplines (boxing, kickboxing, wrestling) for a one-off 'super' fight to see how MMA stacks up against them- but this is something very different.
After watching Gall fight, I'm convinced one of two things is going to happen- Punk is going to bail before the fight ever happens with a serious injury, or they'll use Punk to push Gall as a big name. Expect to see Punk take a very soft defeat if they do fight, he's going to fold quickly.