Only through libvirt, which by design only exposes the lowest common denominator among all supported backends. Docker needs its own native backend for the same reason Xen has its own: so it can do more cool stuff.

See [1] and [2] for more details. It looks like the blueprint just got approved, too!

[1] https://blueprints.launchpad.net/nova/+spec/new-hypervisor-d...

[2] https://github.com/dotcloud/openstack-docker/blob/082fac0c55...