My wife and I started to work with a community not for profit group as a creative consultants for a first annual community haunt. Wolfbeard is correct. Once you expect compensation for your time you open yourself up to liability and could be classified as a business, and required to carry insurance among other things.Our Lion's Club Haunted Hayride and Haunted Barn was strictly volunteer. We had a very small budget for materials and then all proceeds went to charity.
Be very careful in how you structure a non-profit haunt or other business. Be sure to consult an attorney to help draw up the charter and help you understand tax implications, especially if you expect to draw a salary from the enterprise. It can be done, but do it by the book. Some get away with cutting corners, but many do not.
My wife and I provided our services "Pro Bono" with no expectation of compensation for our time and effort. Because we were not hired by the community group, we fell under the group insurance policy and were not required to carry our own insurance or anything else for that matter.
I am not saying that your time should not be compensated. But as Wolfbeard stated, do it by the book to mitigate your risk of liability and avoid tax issues.