I drove ambulances and fire engines for years. Unless a cop observed you and wrote you at the time, nothing is going to happen. I've even had police officers sitting next to me in the ambulance when people have pulled bonehead stunts in front of us. While the officer grumbled about wishing he had his ticket book with him, nothing was going to come of it.
The danger is that if there is an emergency situation in progress, chances are there are "less than essential" cops also responding just because they heard the call, and these folks would enjoy pulling you over almost as much as showing up on the fire/EMS scene.