A black superhero of any kind would receive way more scrutiny and less benefit of the doubt in a majority white setting. The thing that helps Bruce Wayne hide is the fact that he's one of the elites and could be anybody. As others have stated, black folks have been denied the ability to amass and pass that kind of wealth and influence. And in the even there was a black man that was able to get close to that level he'd stand out so there is no way he could pull the secret identity.