http://bgtscc.net/viewtopic.php?f=13&t=78
Those two threads should give you the lore details you were looking for.
For what it's worth, I'm a relatively new player to the UD (been down there a few weeks) and my experiences are apparently different than yours. I've met -maybe- one follower of Elistraee. And this is just an IC suspicion. I've run across more followers of Lloth than anything else, which I've found interesting considering the secular nature of Sshamath.
As for non-drow roleplaying independence, that's normal in Sshamath, according to the lore. Non-drow aren't instantly slaves, they're just second class citizens. African americans in the U.S. 1960s is perhaps an appropriate analogy.
As for lack of charnag/conclave representation, I suppose I agree. I've met more drow that aren't affiliated with the conclave than are. But keep in mind, the PC population need not necessarily represent the NPC population. Just because you haven't run across several conclave-associated PCs, doesn't mean they don't still rule the city.
I can't really comment on DM activity. I've only had one DM interaction (which was on the surface), but considering how large the player base is, that seems normal. That said, I typically notice at least one, if not more, DMs logged on in the UD when I'm on.