Drmark is spot on. I would like to add that worrisome, negative behaviors will influence the dog, but I get a sense from you that is little problem.
The true solution is training ahead of time; CD's are a big help. Even with the best of training most dogs won't handle the extreme situation of the 4th with aplomb, but most WILL be able to make significant improvements.
Sethughes: Giving treats to calm a scared dog almost always results in making dogs more scared. Why? Because it is giving a positive reward to a negative behavior.
What behavior do you want? Calmness? Reward that instead.
Easier to do this before hand when you have more control over the training environment and are able to take baby steps to work up to the desired behavior. Being proactive well ahead of time rather than reactive at the last minute helps bunches and bunches.