In real combat most hits connect with the target even if they deal minimal damages because they are blocked/deflected. Works the same way in PoE, grazes are just those hits that are blocked/deflected and deal low damage, while the misses are real misses (i.e. it never connect with the target). Accuracy in this case define how well you penetrate the defense of the target (block/deflection/dodging/whatever allow you to avoid a full damage hit) not just if you hit it physically or not.
Sounds perfectly fine to me, although I would prefer 1/4 damage for a graze (like you said, a hit that connects but slides of armor or just scratches the opponent) and maybe double damage for crits?