I have done such quite a bit for several years and we had to open some car doors with hydraulic jaws. The number of actual slashed seat belts I did cut myself, witnessed or heard of was zero. That was not due to lack of cutting tools.
We did cut some seat belts in training but I guess that does not count in this context.
OTOH I regularly gave first aid courses and in about every third course there was a person with a friend who personally witnessed someone cutting a seat belt to save someone from a burning car that exploded shortly after. We did not try to verify the claims though .