I haven’t seen this posted elsewhere and I only stumbled on it as I was trying to figure something else out. At present, you have to suggest GPS coordinates on the Find-A-Grave Forums. According to the below information, they are looking at adding this option where anybody can make the change. As long as admins monitor this process, it should be okay, but I am not sure they will do the necessary monitoring to stop the abuses that will crop up.
Map coordinates have not been set for this cemetery. If you know the coordinates, you can suggest an edit on the forums. A feature to edit the map coordinates from here is coming soon.