The only place the battery power goes is from the pack directly to the engine inverter, right down the middle under the car. There’s no way to cut those cables getting through doors or windows, there’s a quick-disconnect in the trunk at the battery back, and the voltage while high (250 voltes) isn’t necessarily deadly with the equipment they are already wearing to do rescue (their gloves and masks and clothes which protect them from heat and chemicals).
There is some training provided to emergency crews, but I’ve not read of any injuries from the high-voltage battery pack.
I have a friend who is on a rescue crew, he has had the training, and he is scared to death of having to cut into a hybrid. He says some are ok and some were not built with any rescue issues in mind.