I worked the 4th of July Fireworks/Parade in 2004. You cannot imagin the crowds unless you have been there. 4th of July is one of our busiest days. We call it a "phase 4" day, that means that the park is filled to capacity. When it was time for the fireworks on Main Street, we had to close down the Teacups bridge because Main Street was filled to capacity. We are talking shoulder to shoulder people, you literally could not move at all. We had to open up our alternate exit which goes behind Toontown and Main Street just so people could leave the park.
Now imagine something that big. It's dark, all the lights are off because of the fireworks. Somebody sees you pull out something large like that, they see an explosion, and hear a pop. The wrong person sees that and panics. You could have a very dangerous situation on your hands. (Of course, chances are that wouldn't happen, but you never know). You also have something that is going to shoot out a substance at high rates of speed in a very tightly packed area. There is a chance, slim though it is, that it could cause injury to nearby guests.
Of course, there is also the issue of cleanliness. After the fireworks, people drop whatever they have. Food, wappers, bags, etc. I have never seen so much trash in my life. Main Street is literally carpeted in trash. Custodial does an awesome job cleaning up between fireworks and the parade, but this would just create a ton more work for them.
My guess is that the official answer will be no, but even if it's not, it's just a plain bad idea.