your homeowners insurance should cover the haunt, its the same as if a trick or treater slipped on your doorstep.
Last year i called the fire department and told them what we were doing. Asked them to come out and take a look and if they saw any problems we would fix it before opening. They had no problems and were happy we called. Thats how you get on their good side. As opposed to them rolling up when you open and saying you have to fix something before people can continue to go through.