It seems like a good idea, but I don't think such a small populous that resorts to crime like that, and isolate themselves would take up all of the lore that Black Marsh offers. I like the idea though. Maybe, you can focus more on 2 separate peoples fighting for the land of Blackmarsh. Maybe the Naga, and the Argonians or something, with some Dunmer influence too?
I don't know much about Aronian culture and lore, so if this doesn't make sense, then just pay no mind.