Found my answer ... grr for seeing it after posting the question.
look at the most recently modified log file that's the name of the affected host.
look for the standard error line
--> stderr: --------
--> Acceptance level of the host has to change from accepted to partner to match with the new imageprofile and proceed with upgrade.
This should explain the failure.
The VIBs I mentioned above show that one was VMwareAccepted and the others were PartnerSupported to pass.