Actually, camping someone for hours is allowed. You need to read the in-game help more. As long as there is a PVP resolution to the "griefing" (in this case, calling on some friends to come help you out would be a PVP resolution), it is 100% allowed.
It's actually a lot easier to grief someone of your own faction (follow them around tagging mobs before they can get em; follow em around and skin their mobs before they can; etc). And no, calling on "Friends" from the other faction to come kill them is not an acceptable resolution to these because there is (theoretically) no cross-faction communication.