The Rock wasn't in the WWE (or wresting in general) nearly as long as many of the other all timers, I think that does hurt him when talking about something like a Mount Rushmore.
Hulk really does seem like the only given. Probably have to go with Flair as a lock if you include all wrestling and not just WWE (or WWF).
After that though, there are so many ways to go. You have the Undertaker, Stone Cold, the Rock, Cena, Sting, Andre, Triple H, Macho Man, Shawn Michaels, Rowdy Roddy, the Hitman, Mick Foley, and guys like Dusty Rhodes that stuck around long after they stopped wrestling. That doesn't even account for actual Olympic style wrestlers like Kurt Angle or Brock Lesnar that had great careers in wrestling.