I have talked to Dommes about this and it is difficult to coordinate two slaves time and donation. Sometimes timing works out. Plus there is discretion.
First one I experienced was a Domme who had a makeshift gloryhole. Nothing fancy but they guys couldn’t see each other. I was the giver. Just had to show up and deliver. Short sweet and quick and headed back to hotel. No donation on my part. Monetarily.
If it is not time consuming for the one party who is really not part of the session it is more doable. It is trying to mesh two slaves and there personalities and kinks that end up not working.