The calculations for hit rate are in Game_Battler 3 i think? The way it's set up by default, attack and skill hit rates have separate but nearly identical calculations-- the skill algorithm factors in whether the skill is allowed to miss. I think the default is
8 * (self.agi / attacker.dex) + eva
with the result being a percentage chance to dodge. So if the target's agility is about the same as the attacker's dexterity, and you're not using the evasion stat, the chance to dodge any particular move is about 8%.