I think the species may all be grouped together in the different classes. Some may generally be on the bottom and some may generally be on the top, but the later Oddworld games will probably be mixing all of them more liberally. The only difference seems like it would be the mindset. Muds are complacent working as slaves until they start getting killed left and right. The defining feature of working muds in the city would probably be just that they're fully integrated into the system--they might be what we would call ambitious, and attempt to climb the industrial ladder.
But yes, natives have nothing to offer the industrial world except labor and habitat, they would not generally be able to help the economy because it uses Moolah, an item of exchange with no practical value (to them)
|