Well technically he doesn’t need permission to make it. He needs permission to release the game. There’s been many mods created that used licensed brands (lots of Disney stuff in Skyrim mods) that didn’t get shut down, Nintendo is famous for not allowing anything though. With DC they’d probably shut it down too if he tried to release it.
Which is why I suggest just doing something original. Make a superhero in a cape with a black suit but don’t make it Batman. If the Watchmen can get away with making owlman guy (that looks exactly like Batman) TS is better off just using a different name and character type.