I recently had a friend show me the gatekeepers. We managed to get up there and tried to start the crystal to no avail. Then we started the raid and I got up there but they are immune to damage. I then attempted to get a crota sword up there but there wasn't enough time to get a sword up there on the exterior path I took. I tried to jump from the orange crystal lamp post on other side and fast sword attack up with no success. There is about a 6ft invisible wall up there on the 3rd story where you can shoot from and be shot at. I had another friend successfully push off one of the gatekeepers with solar grenades as suninger but the gatekeeper jumped back up in about 5 seconds. I'm going to test getting up there after crotas dead and possibly getting a team willing to area of effect grenade push gatekeeper off while trying to kill them 1 at a time during crota battle. The battle is on a timer so if not done fast orgres will spawn. Hopefully this will help the community in working together into figuring out the secret. I highly doubt they are up there as anti glitching spot because they could have made the invisible bumpers higher, adding kill zones, or made the exterior hollow causing you to fall through them if you got up there. But that area is fully acessible and the spawn doors open when you use your ghost. Either there is a chest up there, easter egg or they will be part of a hard raid mode.