A guy a few years back claimed he visited the island
http://shaneperez.blogspot.com/2009/12/discovery-island.html
Uhmmmm......That's normal Florida. It was a swamp, and reverts to same if you leave.
As for getting onto the island, if you can't, you sure are a moron. You can pull a small draft boat right up to the shoreline. If you want to be all commando about it, you can just parallel the shoreline about ten feet from the beach and your paranoid commando buddies can just roll off the side of the moving boat and walk on-shore. What a nut-job?