Yes, I didn't get a chance to check NetBSD's support or not for ZFS by the time you posted your reply:

* https://man.netbsd.org/zfs.8

FreeBSD's graid(8) does appear to RAID6:

* https://man.freebsd.org/cgi/man.cgi?query=graid

* https://docs.freebsd.org/en/books/handbook/geom/