But more than likely, the Byzantines would use it in its simplest form for a long time before rockets and cannons. They would use it in the form of grenade slingers and primitive naval attack. It is never the discoverer that benefits most, it is always the guy who improves upon it, in this case, likely one of the Muslim states constantly fighting against them, or, more interestingly, the Bulgars.
Once more, I ask, if the Arab states discover how to use gunpowder, then how will this effect Iberia? Will Al-Andalus stay for longer or even to modern times?