Gordy-
About 10% of my experience is night unaided. My EMS log varies between 25% and 33% night experience, as usual in the biz it's feast or famine, calls cluster. Night flight is a minority of EMS flight, but in no way exceptional. I'm on the low end of night experience at my program at time of hire, but we had a lot of Army from the cusp of the transition to NVGs.
Which comes to another issue you mention, night checkrides. Perhaps 10% of my training rides since commencing EMS has had ANY night at all. I'd guess that's about to change dramatically as we go to NVGs- fulfilment of that promise was about to expire under statute of limitations. NVGs will make a significant difference in the night accidents purely because we'll be able to see issues in time to DO something about it, be it weather, wires, or whatever.
The issue of pilot error being way more common and dangerous at night won't be resolved by any of the above.