Glad you got the truck stripped of all the garbage and running good. :) I'm sure the residents of your area will apreciate it!
I live in an area where no emissions testing is required on any type of vehilces, at all. My town's fire department is also volunteer and we have no city government, city police, mayor, town council, etc. Everything is County or State here. On the property tax bill, there are line items for fire, rescue and other emergency services, along with school and library services. The fire dept does conduct fund raising events periodically. I do not know other details of their funding.
Since there is no emissions testing here, they could take all the emissions equipment off their fire trucks, if they wished, I suppose. The AZ DEQ (dept of environmental quality) would not know a thing about it.