It specifically states in the FOM to not do it. Not sure DALPA would be on any kind of solid ground to advocate willful disregard of the FOM. The fact is that if you are assigned a seat in the back, as far as the company and FAA is concerned, you are now considered a non rev passenger, and all rules pertaining to jump seating no longer apply. Think of it as an ID0 ticket. Just like all the OAL fight attendants that "Jumpseat" on us. You ever see any of them stop by the front office?
In the end though, it doesn't really matter. Over half the guys don't have a clue what it actually says in the FOM anyway. How many know that OAL dispatchers are allowed up front as long as they are in CASS? Or that even if you have a Delta ID, you are still required to show your certificate and medical?