Accuracy and evasion modifiers have no effect on OHKO moves, so using them was just a waste of time. Assuming Kyogre and your Pokemon were the same level, the chance was still 30% in Emerald as well as all games up to ORAS. (More recently than that, Sheer Cold gained an "accuracy STAB" mechanic, so if Kyogre uses it in a newer game, the hit chance is only 20%.)
