Any email system can be traced, and that will put some guys off. For those who want to participate but are worried about being tracked, Orla, why not have an address where they can post a pen and paper letter to you with whatever they want to say; they can post that from anywhere on the planet and it becomes untraceable if they want to go to the extent of wearing gloves to keep fingerprints off the paper (our prints are all on record here). As I said before, the RYR guys that co-operated with the Dutch TV programme were given up to RYR when the company threatened legal action. I don't think anyone would believe any assurances the BBC gave them over anonymity, at least I hope not - the BBC, despite having many fine employees, has repeatedly demonstrated it has its own agenda and that it is less than scrupulous.
Personally, I think a programme about ME FTLs is missing the point - they are significantly more conservative than EASA FTLs, and the pressure applied to crews to use Commander's Discretion or Reduced Rest is less than in EU low cost airlines. Their behaviour is far more worthy of your time.