Say that I nickname my Pokémon "Arqade" and place it in a gym. Will other players see that nickname? Or will they just see the default name for the Pokémon?
I've seen a picture of "Merica", a Pigeotto that at one point held the gym at the White House, so I'm inclined to think yes. But at my local gyms, I've never seen a nicknamed Pokémon, which makes me wonder if only the original trainer sees it.