The UMC module for managing repository components must only be used with repositories that use Univention’s layout, basically those are Univention’s own repositories (and all of the app center stuff) as well as a limited number of third parties who offer their own updates in this style.
Adding other third party repositories that follow regular Debian repository layouts you simply place a file in /etc/apt/sources.list.d
with the appropriate deb http://…
content. Optionally import the GPG key if the repository is signed (which it hopefully is) with apt-key add …
.
Basically just copy & paste the commands listed on the openhab2 web page you linked to.