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First, yes, the gym leader is able to use Politoed/Poliwrath or the 3 Hitmons if he wants.
Second, you dont have to do anything to change the nick-name. Just edit it in your Team Profile post.
OK, it looks good except for i forgot to mention that you will need to find regular sprites for your pokemon for battles. We have to use sprites that use smaller dimensions otherwise it makes trying to referee fights a headache, so if you could at least paste a separate sprite in your pokemons profiles that would really save a lot of trouble in the future. (The best spot for them is veekun, you can find a list of all of the available sprites they have in the flavor tab near the top of the page. So you are approved so long as you will get around to fixing those eventually, welcome to ASB!