Firemen in the US get paid if they are dispatched to a wildland fire, even if they are volunteers for a city fire department. Not totally different over there, but we have a much larger professional firefighter force.
Mutual aid situations are also paying dispatches, if requested from out of their response area.
When it is not an active fire situation, but prospective employment, an american going to australia to work has visa issues, which is overcome-able, but to get experience there they will likely have to be volunteers until the fire bell goes off, then they may or may not get paid, so is not real attractive to guys paying their own way over in our off season.