> You should be able to see the hosts from ovirt interface.
> I was not able to add an auto-discovered hosts to ovirt it always trows an exception: Failed to add Host <UNKNOWN> (User: admin@internal). probably it is a bug.

Did you add the oVirt provision plugin to Foreman? You probably need it for this to work.
If you did then please submit a bug to oVirt bugzilla.