Okay, so I know the downhill part of skiing with mountaineering boots in 404s is difficult and not very safe.
Are they safer (release wise) with AT or regular alpine boots?

I think that they're more reliable with alpine boots because they don't have an anti-friction device. If they have a sliding anti friction device then they should release with either. With that said, they are AT bindings so they should be fine with AT boots, you just might be taking a chance with your knees.