Wireless microphone systems typically have only 50 mW (fifty one thousandths of one watt!) or less output power. So in other words, they operate with less than 150 mW, which means they are Part 15, and can be anywhere they want as long as they don't interfere with a licensed service. What is 50mW going to interfere with?
Yes, like the article says the sound people need to coordinate and make sure they don't have two mikes on the same frequency.