So I modified a set of Pawel's ZFS-root dataset layout here:
http://blogs.freebsdish.org/pjd/2010/08/06/from-sysinstall-to-zfs-only-configuration/

But since I was using raidz, I merged that setup with the installation-from-fixit onto root ZFS instructions in the wiki here
SEE STEP 2.2:
http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/RAIDZ1

Reboot and system comes up. However, none of my zfs filesystems are mounted through legacy mount:

on boot, all mount shows is:
zroot/root on / (zfs,local,noatime)
devfs on /dev (devfs, local, multilabel)

I have to manually invoke zfs mount -a in order to have them mount, even though yes, they all have static zfs mountpoints set. The filesystem can still run normally without the zfs mounted, as they pass through the root mount. But why is this happening? (zfs_enable=yes in rc.conf, and I can clearly boot to multiuser fine, so bootfs is set properly.).

Here is my fstab:
zroot/root / zfs rw, noatime 0 0
/dev/mirror/swap none swap sw 0 0

Here is zfs get mountpoints:
zroot / (canmount=no)
zroot/root legacy
zroot/tmp /tmp
zroot/usr /usr (canmount=no)
zroot/usr/home /usr/home
zroot/usr/local /usr/local
zroot/usr/obj /usr/obj
zroot/usr/ports /usr/ports
zroot/usr/ports/distfiles /usr/ports/distfiles
zroot/usr/src /usr/src
zroot/var /var (canmount=no)
zroot/var/audit /var/audit
zroot/var/log /var/log
zroot/var/tmp /var/tmp

https://freebsd-users.livejournal.com/124268.html