I just tested this on an fresh LXD Ubuntu Bionic VM and it works:
uname -a
Linux vtest 4.15.0-206-generic
snap install lxd
lxc storage create zfs zfs
Error: Required tool 'zpool' is missing
apt-get install --install-recommends linux-generic-hwe-18.04
reboot
uname -a
Linux vtest 5.4.0-144-generic
lxc storage create zfs zfs
Storage pool zfs created