Dan is right about red dots (AKA reflex sights) being legal. They don't project light towards the target so they are OK.
Laser sights that project an aiming dot onto the critter are illegal.
There is a grey area that I would not risk going into with rangefinding scopes since the regulation states that any sight that projects a light beam is illegal. They were thinking of a laser dot on Bambi's chest for an aiming point but the rangefinder uses a non-visible light beam too.
Lance