I'm glad to see this being discussed here. Unethical workshop leaders are one of my HUGE pet peeves. I lead workshops and private guided tours in Arches, Canyonlands and Grand Teton National Parks. Every year I go through the process of obtaining a CUA for each park (actually, Arches and Canyonlands are covered by one permit), which includes paying the fee, providing proof of liability insurance and CPR/First Aid certification. I've had numerous clients tell horror stories about workshops they'd been on with big-name photographers who didn't have the proper permits and told the participants to tell rangers they were "friends, photography clubs, etc.". It's pathetic and inexcusable.
I've developed a strong relationship with my contacts in the NPS and each year I provide them with a list of photographers who are conducting workshops in their parks so that they can investigate whether they've secured the proper permits. Several times, they have not.
Perhaps slightly off-topic, but another thing that drives me batty are workshop leaders who teach simply because they need the money - not because they find it rewarding. A couple years ago I was leading a workshop and we ran into another workshop group led by a very well known photographer. He was nowhere to be found while his participants floundered. I finally located him, 300 yards away and all alone with his tripod photographing a glorious sunrise. Not at all cool.
As potential workshop participants, I encourage you to ask questions BEFORE you register and pay for a workshop. Ask the leader if he has the permits, then call the managing agency to verify it. Ask workshop leaders to provide you with references you may contact. Definitely check cancellation policies and get everything in writing. In short, do your homework.