Looking at the function that calculates melee hits, I only see one part where ATK is used:
Code:
dmgbonusmod += (float)(this->spellbonuses->ATK + this->itembonuses->ATK)/5;
If that's all there is to it, then it looks like your ATK only applies to a damage bonus.
In fact, I haven't done research on it, but I wouldn't be surprised if ATK from item bonuses is always zero.. ie, I bet this hasn't been coded in yet.