OVS switch type for nmstate managed hosts is currently known to be not working (Bug 1809102).
For this reason the user should be not able to add a RHEL8 host to a Cluster OVS switch type.
Testing has indicated this request is declined. You may appeal this decision by reopening this request.
We don't know what OS is installed on the host on engine before installation, so the only way how to prevent adding EL8 host into OVS cluster is to fail adding it. Also this is temporary only solution until we remove current OVS related code in VDSM and replace it with nmstate (which should happen in one of the earliest z-streams)
Verified on - rhvm-4.4.0-0.31.master.el8ev.noarch
This bugzilla is included in oVirt 4.4.0 release, published on May 20th 2020.
Since the problem described in this bug report should be
resolved in oVirt 4.4.0 release, it has been closed with a resolution of CURRENT RELEASE.
If the solution does not work for you, please open a new bug report.
The Doc Text field looks good,
As for your question - yes, they shouldn't upgrade