Thanks! The FileVault2 driver for Linux that you couldn't find is probably this one:

https://github.com/libyal/libfvde/wiki

It's experimental though. Better back up your data.

I'd recommend to create a partition for ZFS and move data there that you want to use on both OSes, or outright install Linux on a zpool and mount that on macOS. This has worked remarkably well for me, even with lz4 compression and all the other great features. Layer ZFS on TrueCrypt if you need encryption, I wrote a howto a while ago but never had the time to update it:

https://github.com/zfsonlinux/pkg-zfs/wiki/Dual-booting-OS-X...