I'm upgrading our vCenters & hosts atm, and found a quirk in Update Manager. If I am upgrading one host using a custom ESXi baseline, initiated from the Host | Update tab, if then highlight another host in the same cluster and either Check Compliance or Remediate a baseline, I get the errors:
There are errors during the scan operation. Check the events and log files for details.
and/or
Cannot get exclusive access to all required entities. Please wait until all active operations complete and try again.
and/or
There are errors during the remediation operation. Check the events and log files for details.
So it looks to me like if I want to Check Compliance or Remediate more than one host in a cluster, I need to initiate the processes from the Cluster view and cannot do it to individual hosts.
Hosts are all V6.0U3d.