If you want Zeps in game Learn to build one in a 3D editor and make a mod for RoF. Can it be done? I honestly have no idea. Jason seems to think it would take way to many polygons to make it viable. But just as some in Team Fusion over in Cliffs of Dover are designing complete NEW aircraft, I would assume that this is NOT impossible but just improbable. Keep in mind it's not just a matter of building a Zep but working out the calculation for realistic flight.
Most of this is way beyond my understanding.
Build a zeppelin to make a static object = not a problem
Build a flyable zeppelin = impossible without developper help
Build a AI zeppelin = possible if you use an existing flight model, but many problems to solve (animation, damaged model, etc...) because we don't have SDK