Recent medical research in Britain (sorry I can't cite a source other than 'via the BBC') shows that convincing patients that somebody is paying attention (even if it's an actor in a white coat) is beneficial to recovery.
But is it ethical to employ a person with no actual ability to help, even if their presence does? If it's organised by qualified professionals, is that any better? Is there a line between belief in the availability of non-existent help and belief in a different sort of non-existent help? Especially when belief in it helps?