If a player that is alive and goes on the mountain, I'm not sure if this would count because the murderer can still get them. For example if someone goes where olds is right now (http://imgur.com/Eq6aHeD) would this count as map explotation?
Anyone who goes up there is exploiting the map as it is not designed for you to be able to get up there, so yes, you should report anyone you see up on that mountain ledge.