As a practicing attorney, specializing in Criminal Law, I can tell you the following. AEG's don't qualify as either BB guns, or "expanding gas" guns. Nor do they qualify as paintball guns. The guy who posted about "it depends on the officer" is spot on correct. Sadly, we live in a state where it really is the police officers call. What you are doing is not expressly permitted, nor prohibited. Your best bet is to be friendly, polite, explain what everyone is doing, and maybe interest the officer in the gear. Explain that it is all perfectly safe, and it is designed specifically for players to shoot at each other safely. Also note they aren't BB guns, and they don't run off or CO2, they are "merely battery operated". Under-emphasize the power of the gun. If he asks you about FPS, say "I don't know but it doesn't hurt". If you are polite, he'll either tell you to go ahead, and be careful, or he'll tell you to cut it out. If he tells you to cut it out, just pack up for the day.
It's unlikely that you will EVER get written permission from anyone, because they are afraid of liability (rightly or wrongly), should somebody turn an ankle or fall on a sharp stick. Your best bet is to go for it, hope for the best, and be cooperative with any local constabulary that may show up. Please, NOBODY BE STUPID AND BRING A REAL GUN, OR CONTRABAND OF ANY KIND. You would make it impossible for any of the rest of us.
Huckleberry