At the Polynesian, you are MUCH beter off watching the fireworks from the beach at the Polynesian on the other side of the volcano pool or even walk down the beach further.
I'm not sure you can see much from inside Ohana. If possible, I'd have a meal at Ohana, get a drink from the bar just outside Ohana (if you even have room in your body to ingest anything further...) and sit out on the beach. Bring a towell or blanket.