Moved to Mario Kart Wii forum.
Way I see it, it depends on a few things. Certain hacks work in different ways; you might of used a hack or two that's easily tracked by Ninty. And if they pay attention to peoples' cries about hackers, they might investigate the in-game names of those who hack if players who encountered 'em remember their name.
The reason why I say this is that out of curiosity, I did some item hacking on MKW for a single race just to sate said curiosity 'bout hacking. Never got banned or anything. I've helped experiment on some Brawl hackery in regards to wi-fi, too; few of them had any merit, and the ones that did have results definitely never got me banned.