I don't think the UPS, FEDEX or USPS person is any more qualified to determine the hazard and they ship them day in and day out as common goods.
I can see where they should require them to be drained and packaged so they can be controlled. At worst, with the valve off, packed and bagged with some desiccant a spin of a whip at the other end is probably worst case.
I kind of like the idea of embedding them in cartons of household goods but the density will still feel funky when lifted and that could backfire.
I'd escalate it at the moving company, weight of a #35 pound item or even the doubles if you don't break them should be trivial to movers from a logistics standpoint.
About the only thing I can see entertaining is a reasonable density surcharge. Taken to an extreme, if you had a whole van full of these the load, fuel etc would be noteworthy.
If you have a lot of low density stuff, like a big feather collection you may want to have that information handy as a put and take.
Pete