PRP injections seemed to be a promising in patients with osteoarthritis, tendon and muscle injuries but the medical literature doesn't really support it and there is no solid evidence that PRP works any better than placebo. At least this is what I've learned from medical journals I've consulted.
Anecdotally, I heard someone at my place of work had a PRP injection in the knee. It was very painful and failed to give the person the pain relief hoped for.
As to whether the witnesses would accept this type of treatment, I would have to say no since this is an injection of whole blood.