Well, JKR said that there was some ultimate character test that doesn't let people with character flaws become Aurors how the hell did Ron pass that? Or Harry, for that matter. *cough*Imperio*cough*Crucio. But I think that's more about leanings towards Dark Arts or having loose morals, being accepting of bribes. I don't know how she'd imagined that an Auror's characteristics wouldn't change over time, but at least they start out squeaky clean. I believe all the Aurors who worked for Voldemort were in some way coerced, confounded or under Imperius. And I have a feeling that they adhere more to the law and written rules than to their sense of justice if the two happen to clash. But I don't think the Head Auror would turn out to be a Dark Wizard, that's something I'd consider extremely out of the universe. Not that yours runs the danger of becoming one. :P I just remember reading someone's reaction who adheres to canon rather strictly that this would mean that Draco wouldn't stand a chance of becoming an Auror. *shrugs* My Draco would totally find a way to if he wanted to. :D