Yeah, I think a condom is a difficult thing to "forget" but it's super easy to just try your luck while the lady is otherwise distracted. I've seen it happen and so I check every dick that heads in that direction either with my eyes or my fingers.
What i would also do before ever deciding to try out the experience is to attend one as a voyeur to see if that would ne your thing. An sp that i used to know who had frequently been with two guys at the same time told me that she once attended a gb as a voyeur & realized that this wasn’t the type of experience she’d want. So she never had one & told me that she was fairly certain she’d never change her mind.