NO, the nature has nothing to do with what berries you must use, but how much they gain from the pokeblock. Use kelpsy, hondew, and cornn berries for beauty pokeblocks. Only blend in the lilycove pokemon contest hall.
I am a star coordinator, and now all of the nature's likes/dislike of pokeblock flavor. Avoid these natures if you want to get Milotic: Impish, Adamant, Jolly, and Careful. I *think* you can still evolve feebas with these natures, but it is very difficult. You must have excellent pokeblocks. Not only that, but those natures lower sp. atk, which Milotic will use.