does rikku's luck ability help obtain rare items after the battle?

I'm in the thunder plains and i was fighting an iron giant to steal light curtians, and i used the luck ability like 20 times. after the battle i recieved a regen shield. i've never got one from them before. does the luck spell have anything to do with it?

I was quite sure that the Luck ability only increased accuracy and critical hit rate. Could be wrong though.