Does it have to be an evil society? If people have lived with undead for millenia, they're going to be just as evil as people who haven't because they won't know any different. You tell them that having undead servitors is "evil" and they'll look at you as if you're a madman (which to them you are) and run off as fast as their undead-horses - pulled carriages can take them!
Also, its likely to be a continent thing. Not just one country is going to have undead servitors - if it works then every country is going to want one. There could be "modernisation" in "backward" countries so that they had them too - a great way of creating rebellions. Raising the dead is a much bigger spark than rumours of pig/cow fat on rifle cartridges (see Indian Mutiny).
I have to say, I love the idea of Undead Economies. No more muttering from the postmen about never being in when parcels are delivered... Go to Comment
The bloated corpse of a decaying gigantic creature is necromatically enhanced and fused with an undercarriage for use as a grisly and terrifying airship. The methane gas from tissue decay keeps it buoyant in atmosphere, but it can be even more flammable than hydrogen if it escapes...