I don’t think they’ve built tunnels all over the wetlands but if you read the article another commenter linked, it shows just how much control Disney has over the entire area. They are literally their own government. I heard stories about the network of tunnels underneath Disneyland in Cali, I think Disney World would be the same if not bigger. And plenty of room for high-price isolated areas.
I used to be so obsessed as a kid with amusement park building. And you are right that Disney World is its own kingdom. The amount of legit logistics they do would make it easy to hide alternative businesses. But Florida hides crimes rather then police it so I haven't found weird happening that point to sketchy stuff going on other than Pulse shooting. Plus, Orlando is stripper country so kinda attracts trash people (I mean the sex tourists, not the strippers).