Would it pull over if it sees the blinking lights / siren behind it?
Sure. Why wouldn't it? It can detect cars with radar, and see flashing lights with cameras.
I think the hard question is whether it should try to get out of the way, or pull into an intersection to clear a lane (ambulance, fire truck, police), or if it should actually pull the whole way over off of the road and stop (police).
Could you spoof it with a bunch of blinking xmas lights on the side of the road?
No. Putting blinking lights on a car might spoof it, but that will probably get you arrested for impersonating a police vehicle.