I think it depends on the rules being applied. It could be organizational rules like from NMLRA or club rules unique and specific to the host/event. I have two sets of club rules here.
One says, Sights and Sighting Systems - "Any fixture used in conjunction with another fixture for the purpose of aligning the barrel with the target constitutes "sights" with the rear-most fixture referred to as the "rear sight" and the fore-most fixture referred to as the "front sight". Any single apparatus or attachment that is used to align the barrel with the target that is self-contained or one homogenous unit will be considered an "optic", regardless of whether magnification, lenses or electronics are a part thereof. When a single point of reference is mounted on the front portion of the barrel that is used independent of any other fixture or point of reference, for example a "bead" or "post", such point of reference shall constitute a "front aiming point" or "aiming reference".
Kind of complicated but doesn't leave much room for interpretation.
The other club rules are as follows: Rear Sight - any point of reference that has an accompanying point of reference in front of it, each that can be moved or altered to change the point of impact of the projectile on the target in a horizontal or vertical direction. Front Sight - any point of reference that has an accompanying point of reference behind it , each that can be moved or altered to change the point of impact of the projectile on the target in a horizontal or vertical direction. Fixed Sight - a point of reference used for aiming that can only be altered by modification or impact. Post or Bead - an aid to aiming or pointing that is near the muzzle and is permanently secured or threaded to the barrel.
I think this second set of rules and definitions either allows your "rear sight" or doesn't address it and leaves it to interpretation.
Good luck!
