I think there's actually a positive aspect to cemetary caching... when would most of us necessarily visit there otherwise? I think cemetaries remind us of our history are there to remember those who came before us, even if you didn't know them. I always try to take a few minutes to look through the tombstones in the area.
All the cemetary caches I've found have been what I consider respectful. Which is, to me, placed in trees, bushes, or other fixtures that are part of, or surrounding, the cemetary, but not part of a particular grave. I wouldn't personally like a cache that is attached to, hanging on, or alongside a grave marker, or in any decorations that are obviously placed as part of a person's memorial. At least not if the Cacher that placed it doesn't know the deceased. I just think of the family and how they would feel about us rooting around by their loved one's grave.
Granted, some of us would be *all* too happy to have a ammo box for a head stone. And if that's how you'd like to be remembered, go for it.