Actually I've been thinking whether it is legal at all. It probably is if it takes place outside the cemetery, but perhaps they can be seen as disturbing the peace. I really don't know how far you can go with this. :dunno:
My guess is they asked some idiot lawyer they have on retainer before they did this.
They apparently have done similar things before so they obviously have some experience with it.
Never underestimate the resourcefullness of religious nuts.