The question at hand is not can an omnipotent God have heard a prayer, but rather who were they praying to?
What/Who do you pray to, when asking for success in terror, and suicide?
Oh, I’m sorry, I thought you asked if God heard their prayers.
Whatever the hijackers were praying to, I doubt those not present (like other hijackers or hostages) heard. But I do not doubt that God heard them!