Rumors about this have been floating around for years and are often used as a reason to have the auto tips removed and pay them in cash on your own. But then anyone who thinks the stewards, waiters, and busboys aren't paying a little extortion money to their supervisors are fooling themselves. In either case, I don't think it is any of my business and it is between the crew and the company.
I doubt that a senior officer of a ship would suddenly blurt out confidential accounting info to a passenger. If it were a fact I am sure disgruntled crew members would have spilled the beans a long time ago and it would be common knowledge, and not something hidden in a four month old thread on Flyertalk (which is a sister forum to ours, also owned by Internet Brands).
If it is true apparently the crew is okay with it, since Princess has no problem staffing their ships and everyone seems happy.