'OHana runs notoriously late in seating. It is likely you will not even be seated prior to the fireworks. Anyone sitting at a window table with a view at 8:30 for 9:00 fireworks is staying put until after the fireworks.
There are only a very few tables with a good view.
I believe it is reported that the Poly beach access is limited to Poly resort guests on July 4th, so that will not be an option either.
You may get lucky and be seated at one of the few window tables in time to see the fireworks, but I strongly doubt it.