- 3 Hosts
- vSphere Server is on one of the hosts
- Update Manager can not update this host, since vSphere Server needs to run on it
- Essentials has no DRS feature (as far as I know) to move tha appliance to another host
How should this host be updated?
Shut down vCenter Server (there is no such thing as "vSphere Server") and patch/update ESXi from the command line (please use search).