It's not necessarily about actual 'treatment' though, is it, it's about making someone who is in the most difficult part of an illness feel more relaxed, better etc. Cancer treatment is brutal and anything holistic that can help with that is surely worth spending money on?
When I had chemo a couple of years ago, there was a Reiki lady who came into the unit and did treatments either in the chair or in a private room. At no point was she ripping out IV drips and insisting that the reiki would do the job instead 