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
A fey spirit masks itself as a bee which investigates all who travel within a specific section of the forest. Any the bee finds worthy are allowed to see the hidden opening into the fey kingdom, just off of the trail. Any deemed unworthy see only the bee, buzzing around around them momentarily before moving on.