Very true. The pressure is far too great. If they are somehow able to get the coffin open, the dirt will pulverise their bone structure.
However, most buried afflicted individuals are too thoroughly dead to become animate.
So yeah, cemetary is pretty safe as long as it's a conventional graveyard. If they have one of those fancy deals where they keep the coffins stored along aisles of marble wall slots though, you're pretty screwed.