If your kernel is doing any caching and it’s shutdown without a chance to flush its caches, then doesn’t it necessarily have the possibility of corrupted data?

No. ZFS is well-renowned for a reason, it's very resilient. The chance of a power cut ever inducing any actual data loss with ZFS is astronomically low. https://superuser.com/questions/1134753/can-zfs-cope-with-su...

I'm not so sure. Most filesystems don't come with ACID guarantees.

They should. ZFS is roughly the filesystem equivalent of an ACID database. It's incredibly resilient to power cuts. https://superuser.com/questions/1134753/can-zfs-cope-with-su...