Never played in a decent pro am before, only small ones with local pros, I've been to the Alfred Dunhill as a caddy but that's more a celebrity thing.
They did ask for an AGU handicap, not sure if it was compulsory or not but didn't seem to be any need to be under a limit. In this case the cost of entering is so high I doubt you would get anyone that didn't love their golf, so you'd expect most people entering would be at least regular players.
I don't hit the ball as well as I once did, but I can still get around reasonably, be lying if I said I'm not already nervous about the prospect of teeing off in front of a pro though, especially now they have decided to let crowds in!