If a speeding ambulance hit a civilian car would the ambulance be obliged to stop?

"Speeding?" Did they have their lights and warning devices activated?

If so, they may have been either responding to a critical incident call or were transporting a patient to a hospital. Under those circumstances it becomes a judgement call on the part of the ambulance crew. If the ambulance is mechanically capable of proceeding, AND the damage to the other vehicle was not life-threatening, they might continue on their way. They obviously would have to report it as soon as they had their first opportunity, and may even return to the scene of the collision to assist in the investigation.

The same question could be asked about ANY public safety emergency response vehicle, and all such incidents must stand or fall on their own individual merits.