Would it matter? Isn't it rather the point that you don't know who is on the other side?
Absolutely right Ivor - I personally don't care what I shoot my load into, and have visited many a glory hole, as I like the thought of wondering who, what and sometimes which hole I have cum into.
But others might only want a woman on the other side, hence my comment. And crucially, others may not have thought that it may be a male arse they are fucking or male mouth giving them a BJ.