I wonder what the international (or national) law would be if UFC did take over an island somewhere. They could pretty much do whatever they wanted, unless the jurisdiction interceded.
When the UFC puts on events in unregulated locations they act as their own commission, following the rules of the Nevada commission or the rules of Association of Boxing Commissions (ABC). They hire experienced judges and licensed referees that would normally be used in regulated places like Nevada.
The UFC already contracts out to the United States Anti-Doping Agency (USADA) to do what is basically olympic level drug testing of all their athletes.
There are unified rules for MMA, set by the ABC. The UFC very much wants to be legit and legal, so "whatever they want" will be following established rules and regulations.
The governing bodies are utterly toothless. What would be the point of "banning" anyone involved with the world's premier MMA organization? Then they'd have no work to do, and no purpose. Nevada needs the UFC more than the UFC needs Nevada. Remember, MMA was banned in New York state for a long time, so the UFC held events elsewhere. Who loses then? It's a weird captured relationship.