Would it be illegal to allow the player to load images into the game, such as a logo for the WCW ring, as well as giving them the opportunity to create an exact replica of their favorite arena? Not having the exact pieces available to use, but say, letting them make the pieces themselves? Could that be a valuable loophole?

You'll still be vulnerable and liable for it, since it's you who set up the game. You should write a TOS that forbids the use of copyrighted and trademarked materials, and you should be prepared to kill such materials when requested by the IP owner.