It gives a good look at how said MPs operate. It's not technically slavery, though is not much better, generally. I don't know about too many of these MPs being that near the dome, seeing as most of the surrounding terrain is pretty barren.
As to the topic of slavery, it most certainly exists, though not legal. This at least applies to areas under Withmore jurisdiction. Still, the law can't catch everyone, despite what they may claim.
So, yes, it is entirely possible to have a background as a slave. And yes, such a slave could be used to work a plantation, among other things. It a world where even the "free" are treated as an expendable commodity, the life of a slave would be that much harsher.
Also, if anything you write in your history doesn't quite jive with lore, the reviewing gm well that you know and point you in the right direction, so don't be afraid to take a little liberty when writing.
