conclusion..

the driver had ~5 second to react after he heard the siren and clear visible of LED Light on top of the ambulance. (0:18 of the video).
The video clearly showed that he had ample time to react and to notify the ambulance. Even the v.recorder managed to record siren 5 second before impact.

yes, the ambulance still need to obey red light. Other 2 lanes on the right side of the driver already slowed down, congested and given their way to ambulance. If the driver is paying more attention to surrounding, the driver should slow down and look for emergency vehicle coming from any point of the road. even the ambulance could be flying and land from the sky. he should be aware.

even on empty road,, please pay more attention even your way has the green light. Remember the singapore ferrari and the lexus cases..