Guess it's true. Give someone an ounce of power and it goes to their head.
This better be some world changing, CEO type level job this guy may be promoted to, otherwise the level of nitpicking going on is completely unnecessary. OP's concerns sound so typical of the middle manager trying to play God instead of focusing on the bottomline. If the bottomline is how he looks, and your company's goal is simply image over quality work, I guess he should be gone. If the bottomline is quality of work and satisfied customers, then it sounds like he's a decent employee, who reportedly has a lot of potential, so why not give him an opportunity to show you how much potential he has?