I've got a few in my family lines, who died in the 1750's, that were "dug up" by archaeology students at Wake Forest University, in the 80's. It was a "Strangers Cemetery" though; no one knew it was there at the time, the roads had changed, and the village was long ago abandoned. I guess the answer depends upon whether the grave site is tended to in any way. "Unknown' burial sites appear to be fair game.
I'm going to have myself embalmed, and in a plastic coffin of the kind they use to store nuclear waste. I'll have my fingers in the FU position, and a t-shirt that reads, Rest in Peace means Rest in Peace, you A**holes.