Now that could be considered like saying, "Infantry and Artillery do not get along" when in reality it's usually a few bad apples ruining it for all. The larger the city, the greater the amount of apples. It's a generalization and while not entirely incorrect or unfair it still does not speak for the services, or models of delivery, as a whole.
In Canadian cities we can see examples of many different management systems. The one mariomike points out is just one. We also have integrated services that see staff members who are dual qualified and, for the most part and from my understanding, split their time between EMS and Fire Rigs (ft McMurray would be a good example)
We also have places like Nova Scotia that have a provincially (of sorts) run EHS system of ambulances, stations and MFR training programs for fire fighters. The ambulances respond the same as they always would have but have the added sets of hands from a responding fire engine/rescue. The firefighters jobs are to perform critical interventions (Like CPR/AED or the like) but otherwise serve as a medium to gather information until EHS arrives and they also have that "intimate local knowledge" that aids in situations like needing air ambulances but also helps when we have to deal with a distraught family member as we so often know them personally. And then, we're also muscle - a two person ambulance trying to haul out someone who's 350 lbs. and unconscious....yeah. It's amazing to see this system at work from the calls to the training modules held by EHS and hosted at fire stations to the equipment placement done for free by EHS to hopefully improve the overall pre hospital care that someone could receive.
Perhaps the most interesting place I have been in this country to see, well, a gong show was St John's back in the late 90's and early part of this century. The City of St John's Fire Department not only put out fires but had ambulances placed in certain stations. The Health Sciences Centre had their own ambulances as well and many a time both services would be dispatched to the same call which, inevitably, brought some bad blood to the surface. I had the misfortune of taking some EMS related courses from two instructors - one from the HSC EMS, the other from the City FD EMS...wasn't hard to see their disdain from one another done in the way of sniping the other guy's previous day's teachings (while he wasn't there, of course) I have no clue if this has changed or not but this is what I saw back then.
To pbi's original question: I've seen it all in regards to how composite departments get along and I think that, for the most pat, it works well. But again it comes down to a few individuals or a small group of individuals who make it bad for everyone. There was a certain FD a few years back that just could not keep themselves out of Frank Magazine (an illustrious feat to be included in those pages) for all the bickering that went on between the paid drivers and the volunteer firefighters and officers of the department. Suffice it to say that each side had its points and each side also did its level best to piss on, or off as it were, the other. Today, from the outside, they seem quite happy and able to work together but there were some big changes before that happened and a few people disappeared.
As someone who has had to work in a paid role alongside volunteers I will say this: My largest concern is safety, levels and standards of training, physical fitness. Most of the volunteers I have met and have volunteered with (yes, I have worn both hats though have never been considered a Two Hatter) have been regular people who just want to help. They attend training sessions, they fight fires, they know their limits. Then we have those bad apples. I will not get into sharing horror stories because the cold and simple truth is that there are thuds-a-plenty in the full time ranks as well. And really, what does it matter?
The thing to me is that we sometimes have a group of paid guys who just don't like volunteers and will do anything they can to express this. Sometimes it's the volunteers who act out and decide to make themselves, and their opinions, known. We also have Officers and Chiefs as well as administrators who will do nothing about this because of the intricacy of the matter. Then we have the higher ups within the municipality who are sometimes as much to blame as the guys on the floor. It's a multi headed beast, this composite department thing, and each and every one is different.
You know, if more of the fire and EMS types, no matter what their employment situation or working conditions, learned to turn the other cheek from time to time it might just get a bit easier. And speaking for the fire services as a whole, we'd also gain some credibility as and among professionals. Too bad the minority still wants to focus on Kingdom building, cliques and petty arguments. Tradition unimpeded by change.