Some bands get spooked with the red recording light on.
If you have that red emergency light flashing while recording it might totally chase the good vibes away.
However, if you can fit a lava lamp on the back of the fire truck then it should work fine.
I have an image of an challenged engineer calling 911 and then having six of these trucks fitted with mics speeding up to a drum kit- sirens on and red lights flashing. ...The studio first responders.