Other than the improbability of 5-6IV legends and perfect hidden power stats on them, as well as pre-gen VI transferred pokemon with perfect IV, a hacked pokemon can completely pass off as a legitimate one. The only thing that would break that is if the user admits to using hacked pokemon, even so there is no difference other than the opponent possibly being butthurt that his days of grinding is indirectly made light of through another person's few clicks and keystrokes. With that though, the opponent should just suck it up. I'm speaking as a hacker myself. Even with hacked legends, the bottom line is usage with the lingering possibility of hax or RNG, whatever. If a person wins with legitimate pokemon, it's not because the pokemon are legitimate. There shouldn't be an agreement over hacked pokemon usage, after all they too adhere to the wifi checks, which is why you don't see full on hackmons like a Sturdy Shedinja in Battle Spot.
I got really sidetracked, but I don't like the high horse talk of legitimate players over hackers. Different paths taken to the same goals, and it's not a race in the end. Besides if Hyper Training isn't a pain to do, the hackers vs. legit players thing could be rendered close to being moot.