No, ZoL bypasses the usual page cache.

Is it doing it for mmap though? 2 years ago, it didn't double-buffer apart from mmaped files. Here's a note about priorities: https://news.ycombinator.com/item?id=11697901

Also seems to be solved in this port: https://www.crossmeta.io/another-zfs-port-on-linux/

Given that said port predates feature flags and has no source posted, making any assertions about what it actually does versus claims to do seems premature.