Lasiorhinus, I think you will find that in NZ, instructors generally do get paid, crapily but still paid. I've never heard of a instructor or drop pilot in NZ work for free like they do in Oz. (Hard hat and flak jacket.. ON)
However, the ATC National Aviation Camp and the Air Training Corp is a non-profit organsisation.
This is no different than any other charitable, community work. You are not left out of pocket attending this camp. They pay for all food, accommodation, and provide access to a top notch bar.
We're not talking about dropping parachutes for free and a commercial operator getting the money. These students/cadets have all worked hard and been awarded scholarships from high profile aviation companies to attend this camp.
I would happily renew my C-Cat rating and instruct on this camp, however I have the same problem as XRNZAF, my boss won't give me leave. January is our busiest time. I had a rewarding and fun time instructing on these courses.
Though it sounds like I will have to try and make a appearance into BHM to farewell FML and the Padre...
Instead of being focused on the money, how about giving something back to the community that has fostered many a young person's interest into aviation.