SawMan, I'd be interested in any specific references you can give to such an assertion relating to motorcycle helmets in particular. We (motorcycling advocates in Australia) are completely unable to get any comment from manufacturers either for or against stuck on camera mounts. They use (as in Schu's case on his ski helmet) double sided tape, with no penetration of nor modification to the helmet shell save for the adhesive.
Whereas CEP plugs require a hole to be drilled into the flying helmet shell, Bluetooth installations often require a hole into the motorcycle helmet shell or the edge of the shell and compliance stickers are attached with an adhesive. Certainly the bluetooth modification and the compliance sticker are with the approval of the helmet manufacturer (in my case, BMW).