Aha, I thought so. But not in [Caution:off topic for a moment] PC-BSD using Geli to encrypt whole disk - it wants you to enter the encryption pass wordings for both disks, one at a time, at boot up - so when 2d disk failes, not able to enter 2d password and entire boot up stops and drops to grub "rescue" mode. Some Ubuntu user posted some elaborate intramfs script for similar problem that happened on Ubuntu under similar circumstances. Will see soon enough on Mac, later next week when having time.
On Mac I forgot to mention that it seems, after entering the Filevault2 password, disk icon not appear on desktop until you type: sudo zpool import mypoolname,
and you got to enter sudo zpool export mypoolname when you are going to disconnect zfs disk.
Still taking baby steps till getting more comfortable but the range of options and things you can do seems REALLY powerful.