First of all, I figured out several years ago that there is actually a difference between a medical session and nurse role play.
I'm glad that someone makes a distinction about this.. Sadly, there are some that are not clear about the distinction between the two.. Maybe that would explain why you have met individuals that bawked at the idea of showing you tits?
To me, the flash of a tit goes along the lines of the kinky nurse roleplay, which based on the number of fetish outfits I possess, I have no problems with that. But, I can understand why one would not, particularly if they are strictly dominant and not conducting any type of roleplay into the session.
You are right to ask the Domme prior to play because not all are fully equipped to handle every request it takes lots of room, costs for toys, etc.. I used to be, but find that a small amount are interested. Enema play is never a problem, and I have lots of medical equipment still, but not very many are interested.
The majority prefer to talk, rather than walk & piercing is a interest that you may not be aware of.