Yes, this is true. If you cup your hands and enough people do it, it will slow/stop the ride. Bad thing is, is that when the ride is over, you are kicked out of the park. They are very serious there about that kind of thing. My friend works there.
i had a talk with one of the ride operator chicks while i was stuck on the iron dragon for half an hour... she was really nice, and from MI too ! she informed me on that ride cause thats the one she usually works i guess. either way, i'm there!!! hands down of course