Firefighter/paramedic here. These are definitely outlier events. It's not zero risk, but it's close enough to zero to not worry about.

That isn't to say violence against Fire/EMS isn't an issue, but the idea that we need cops on every call just in case it's an ambush is silly. One of my first priorities on a scene where there are cops present is to clear the cops as quickly as possible. Nine times out of ten if a cop is going to get involved in something, they're going to escalate things, not cool them down.