I've never been a volunteer patient but have been asked by my general doctor if it was okay for a female doc-in-training to be present while doing an annual physical exam. I've been going to the same doc for years, so he knows I'm totally smooth with piercings and tattoos down there. I think she was a little surprised when she saw my decorations, but was totally professional. As he was examining my penis and scrotum, he asked if I cleaned my foreskin regularly. That was kinda cool because my foreskin is restored.
I've done this bunches, including having a female student present while I got the ol' cotton swab right inside the tip of Mini Me. Did this for my PCP, two of them, and actually had told them both at the outset that (1.) I have no fear of being naked in front of 1,000 people or more, (2.) to EXPECT me to "go there" at every appointment , giving graphic details of my every everything based on my issues and/or his queries, venturing far deep into the land of TMI if it was in the general public - but this was his job and my health / life, and doing less is just a waste of time and money, and (3.) if there was ever any assistant or student or whatever he might have who could benefit from being present to learn, no need to ask because I am already telling.
I am in a unique position - just due to my inherent nature as generally willing to be both inwardly and physically naked - to help people gain the education and training they need to become (or maybe become better) doctors. They, in turn, will lay hands on who knows how many people in what sort of need and where in the future days.
There's really no question to it.