My speculation on this Lost Sector was always that the whole facility(including all the buildings outside) were part of a small "city" run by the Spider. I assume when the Scorn pushed the Spider into hiding, House Dusk saw an opportunity to loot the Shore. This Marauder likely found The Empty Tank and set up shop. Fighting that Captain before fighting a Vandal for the last boss(definitely their leader)makes me think that these Fallen might have decided that they could defect and live a comfortable life of crime in their new bar. The Marauder as their "Kell" because he found the place.
Same here. The lost sector during a powerful engram quest was mentioned as the “Heart of the spiders web.”