No Problem.
You have both.
You have a host, Univention Corporate Server - A Debian System - Debian is a Linux distribution, like Ubuntu.
On that you have docker - a virtualization software, like Virtual Box, but without the graphic Interface
And ownCloud runs as a Docker container on that Software on your host.
In summery
{Appliance
[UCS Debian
(owncloud docker)
]
}