So we found out while waiting for a sixth person at the Gatekeepers that it is a pretty great glimmer farm especially if you have a large group. You'll need at least 3 people to open the door but with Blue Polyphage and the ~20 "major" enemies you can very quickly build your bank back to 25K. For every 20 you kill you get 740 glimmer. We were playing on hard but I believe that they are majors on normal also. Never seemed relevant but if your Iron Banner group is low on funds it may be a good option. Good Luck!