Given how fast a Zamboni goes I think that would be the world's most avoidable accident.
It's not uncommon for people to be killed or seriously injured in collision with a stationary object. Slow moving vehicles are probably more dangerous in some circumstances than speeding ones.
But if it did happen then my insurance company would pay. I've never filed through someone else's insurance and I never will. It's always WAY more hassle than it's worth. I trust my insurance company. I'm not so sure about the other guy's.
I don't know how it works in the US but here you would claim on your own insurance in the first instance. If the law is not involved the insurance companies then apportion the blame between themselves. If it's not your fault you pay nothing & lose no benefits - in theory. That's assuming that all interested parties are insured of course. I doubt that these two idiots were covered by any form of insurance.