I honestly think that GUE has as big an impact as a tiny organization can have, in protecting reefs. Not only are GUE divers trained to maintain buoyancy control (even under stress, or when working) and avoid contact with reefs, but GUE as an organization has enough of an interest in reef conservation that, not too long ago, they decided that every penny from their basic membership fee (or the first $39 of ANY membership level) would go to Project Baseline, which is an effort to document the current status of the underwater environment, so that we can truly know if things are changing, whether as a result of diver sunscreen or the huge sediment loads that come with the grading of a new golf course.
I do share your concern about the lights we use. I try never to direct an HID light at a single individual animal for very long, without covering the light with my fingers to diffuse and reduce the brightness. I don't like HID lights in MY face, and I have eyelids. I don't think octopuses like them, either.