I don't think that simply being a firefighter gives you much of an advantage at all. Yes, firefighters will know about fire behaviour, neutral layers, flashover, backdraft etc, but as inspectors our intervention and influence is well before that. By the time things like flashover are likely the 'relevant people' are stood outside the building watching the firefighters go about their jobs.
Buildings have been designed by non-fire-service-staff for years. Remember it is Building Control who ensure that Part B is met, and Building Control does not consist of firefighters. (Granted, many BC bodies rely too heavily on FRS input for part B matters, but some are quite capable)
In the days of the FP Act when firefighters were tasked with fire certificate inspections, then this will have been a good grounding in fire safety that would have been to their advantage in any shift over to fire safety. But give this same task to any civilian and it will be just as useful for the civilian.
I believe that the main problem to be addressed with civilian staff doing FP is the potential for ops to lose their fire safety knowledge. I am sure many of the ex SC's ADO's here will have used their own fire safety knowledge to their advantage when taking control of an incident at some point.