Šimon,
According to [1] oVirt should be accessible through IPv6 address.
From my experience engine web&rest can be accessed by using an URL with an IPv6 address in a browser.
Please notice that an IPv6 literal address (not a hostname
that resolves to an IPv6 address) in a valid URL should be wrapped by
brackets, e.g. http://[1::2]:80/path.
You can verify that the engine listens to an IPv6 by running the following command from the Linux console of the host that runs ovirt-engine (while ovirt-engine service runs):
where <port> is the port ovirt-engine should be listening to and be accessed through (default is 80).