You are welcome to do so...however, these areas are very popular, and will likely be full for fireworks viewing, making it a possibly unpleasant experience unless you arrive early.
I think the only real indoor option you have is drinks in the lounge at the California Grill at the time of the Magic Kingdom fireworks. However, access to the restaurant is restricted. You either need to have a reservation or be allowed up by the second-floor check in desk at the Contemporary resort. No one goes up to the restaurant on the 15th floor without being cleared by the desk. If the lounge area has space, they'll let you up for just drinks, but if it's full, you probably won't be cleared to go up. The closer you get to time for fireworks, the less chance you have of gaining access. Usually, people who have been seated at tables in the restaurant keep the tables until after the fireworks, and the lounge fills with persons with reservations who are waiting for those tables to be vacated. I'd arrange to arrive early and stay in the lounge until the fireworks show. The area of the lounge with tables and chairs that might have fireworks views is really quite small. The restaurant has an outdoor observation deck; if you happen to get in, you can watch from there if you are not by a window.
The Top of the World Lounge at Bay Lake Tower resort has fireworks viewing. However, it is restricted to Disney Vacation Club members staying at Bay Lake Tower and their guests.
If you don't mind going outside, some like to get drinks from the Tambu Lounge at the Polynesian and take them outside to the beach for fireworks viewing. Although you can see the show from inside the 'Ohana restaurant I think the view from the lounge itself is pretty limited.
You can see the fireworks from Narcoosees at the Grand Floridian but I do not know if they have an area for drinks only...I think they have a small bar area. I'm pretty sure you'd have to go outside to be able to see the show.
Epcot's fireworks show, Illuminations, is not generally viewable from the resorts nearby except for the high fireworks (quite a bit of the action in that show takes place on the surface of the lagoon in the World Showcase) and then only if one is outdoors.
