Since this site is mainly about programs, I will put this in to the context of the program I was in and the group therapy method they used.
We mainly had "Raps" for our group therapy. And the poster for this thread suggests that there is some benefit to having other opinions or personalities involved to give a more broad critique to a participant. In our raps, generally the other participants were coaxed and coached on what feedback to give. Those who had been there longer had learned all the program lingo and packaged lines so they might not need as much coaching. But the Raps were not voluntary, the critique really came from the staff and not the students, even if the students were the ones saying things. It was the staff who directed, controlled and determined what was to be said, how it was to be said, what the student should feel, what the student should say in response, when the indictment began and when it ended. Add in the fact the staff running the group therapy had no education, background or experience in counseling, psychology or therapy, I would argue the group therapy held little value. And as these sessions were generally just loud, verbally abusive scream-fests, it was difficult for students to feel anything other than assaulted, against their will, unable to walk away as staff either screamed abuses or directed others to do the same.
Additionally, whereas a druggie or alcoholic might be able to spot another of their kind, these people can hardly be objective in critiquing anyone. I would not even trust the judgment of a PhD holding drug addict to be objective and provide reliable feedback, even if that PhD was in Psychology. So relying on people with similar experiences is a bad choice.
Also, in our program, attractive females had the hardest time of it. Any suggestion of being attracted to others was not only frowned upon, the female in question was likely to have endless abuse heaped upon her, had probably been called a whore, slut or worse many times by staff or by students directed by staff. Thus, relying on this attractive female to give truthful statements about her opinion of some guy her age with low self esteem issues would be problematic at best. And I would not imagine her offering to provide her insights willingly or enjoying the unprovoked and un-asked for attention of being put on the spot to have to say something possibly derogatory to her fellow student, knowing from first-hand experience what it is like.
This is not to say that some level of psychological-based role playing can't be of some therapeutic value, but by itself it is almost worthless and should not play a large role in a therapy setting. Many licensed therapists will act out the persona of someone in the life of their patient in order to allow the patient to pratice speaking to that person, or to vent feelings and frustrations towards that person. But this role playing is never the core of the therapy. But in the programs, it is central and unending and mostly just confrontational.
