So, no exemptions for anyone, but then part of the cost of running an ambulance service is paying speeding fines regularly. Given the cost of ambulance services without that, the additional expense is lost in the noise, making it obviously a good choice to speed when useful (for ambulances).
Trying to figure out after the fact whether someone had a good reason to break the law (and therefore shouldn't be penalized) is one of the things that complicates legal systems enormously. Instead, we should write the law clearly and specify the penalties for breaking it directly, and let those who have the best information about the situation, the potential lawbreaker(s), choose whether it is worth breaking the law in a given instance.