People hacked the hell out of the 360 version and wasn't banned so I doubt it'll happen with GFWL, which Microsoft seems to care less about.
I was one of those people but I tried to prevent PvP. If you receive no complaints it shouldn't be a problem.
There's no "trying" in preventing PvP if you're cheating. If you're cheating, you play in offline mode exclusively with that character. Period.
People who actually PvP in this game are generally honorable, and it's a common courtesy to praise the sun or bow in sight of your quarry (or your hunter) for a gentleman's duel. Sure, a lot of the game's mechanics and features encourage you to be a ruthless sociopath about PvP, using AI enemies and rings that make you impossible to lock onto in order to score a kill at all costs - but the most important part is that everyone can benefit from PvP. The Dragon covenant, the Darkmoon Blades, etc.
So please, everyone. Don't think of cheating online as a question of whether or not you'll get banned. Think of it as whether you'd like to genuinely ruin one of the most fun portions of the game for everybody else.