These outfits are run by Earth Firsters, Tree Huggin' Hairy Legged Bark Biters. You will spend a week being lectured about the evils of your carbon spewing ways, and have to listen to some twenty something telling you how pristine this place was 20 years ago before global warming killed off the Humpback Chub(like he was there). Then will come the rant about aircraft destroying the "Natural Quiet" of the Grand Canyon.
But later in the evening he will fire up a joint and pass it your way as a peace offering.
Sorry, I don't have any usefull info for you. The Grand Canyon is a beautiful place. Unfortunately, radical environmentalists think it is their personal playground. But please don't let my cynicism dissuade you from going on a rafting trip. IMHO You would definitely be better off going on a motorized trip. That way the spectre of hypocrisy might keep them from giving you too hard a time.