Delta and United both ahve the same policies right now, they will accept as many offline jumpseaters as there are jumpseats in the aircraft, but you must be in uniform and on the reciprocal agreement list. You cannot occupy the cockpit jumpseat and must have a seat in the back. You will be the last priority for boarding, after all rev and non-rev passengers. Despite this I haven't had much trouble getting around. Good luck!
Twotter76