I recently became aware that there are some paid departments out there (seem to be a lot in California), with what they call Reserve programs. They seem to often use these as a way to evaluate potential new hires though there are those who participate in the programs who aren't interested in a full time job. Although the details vary, they often require Reserve firefighters to have the same level of training as the paid firefighters and work a couple of shifts a month or a minimum number of hours, usually riding with the paid crews.

It seems to me that in combination departments that "Reserve" might be a more appropriate name for the "volunteers" since it would seem to more accurately describe their function.

Although this is really more of an issue involving the training standards and functions of volunteers in combination departments than it is involving stipends for volunteers, if your combination department does give stipends to volunteers, using the term "Reserve" might help reduce some confusion that can be prompted by "volunteer" in that context.