I was out there a few years ago with a buddy when we came upon a patron suffering from heat stroke. We rendered first aid while a staff member went to fetch the medics. I figured it would be one of the metro EMS agencies under a contract with the festival, but it ended up being two young men in costume that carried the victim out on a rickshaw. Apparently they cart them off to the edge of the property, off set, where EMS makes a meet. I did not see any radios on their staff. So I think to maintain authenticity they communicate with smoke signals, hand gestures, and voice relay - your scanner may not do any good