In my experience, human player controlled hidden nationality units can't capture cities. AI controlled hidden nationality units can do it very well thank you. And they can capture workers and stay stacked with them so you can't attack them without declaring war.
And the warrior/workers: you could make the "clear wetland" animation their attack/defense--swinging away with a machete. These would be "hardy workers," I guess, and cost more shields. How far off is this from reality?
As for a UN unit, why bother to upgrade? Why not just have the UN make a hidden nationality, maintenance free, 1 attack Mechanized Infantry every turn? Except the UN should be buildable only by a Democracy government, not a Republic type government, so if you went to Republic the UN would stop working until you switched back to Democracy.
And the warrior/workers: you could make the "clear wetland" animation their attack/defense--swinging away with a machete. These would be "hardy workers," I guess, and cost more shields. How far off is this from reality?
As for a UN unit, why bother to upgrade? Why not just have the UN make a hidden nationality, maintenance free, 1 attack Mechanized Infantry every turn? Except the UN should be buildable only by a Democracy government, not a Republic type government, so if you went to Republic the UN would stop working until you switched back to Democracy.