I just finished the Polynesia DLC scenario as Tahiti and received the achievement for winning as Tahiti AND for winning as Hiawatha (I hadn't played as him before). I'm assuming this was because they used Hiawatha as the leader of Tahiti.
I don't have a save file or anything, but if you look at my achievements and search for Mar 6, you'll see I got both of the achievements at the same time.
I don't have a save file or anything, but if you look at my achievements and search for Mar 6, you'll see I got both of the achievements at the same time.