I would point out that about 10% of known historic trade guns had a rear sight. If you choose not to put a sight on your trade gun, I would think you shoudnt shun those that do.My vote is no. That's like having a trade gun match and some guy is shooting a trade gun with a rear sight, it does make a diffidence.
That said I’ve never tried to bully my way in to a smoothie shoot, and have shot against rifles instead of ‘fair’ guns.
I ve never entered these. So don’t have skin in the game. You who do are dependent on people’s honesty. It would be too easy to cheat. Since it’s just for fun why worry if Joe needs a peep to see well enough to shoot and Bob can see well enough to shoot with out them? Unless Joe resembles a smelly body part who only wants to win no matter what, he wouldn’t be sticking one on his rifle if he didn’t need it.