Good to know, and thanks for the command line link. I inherited two standalone ESX 4.1 servers with no vCenter. I convinced the client to upgrade to Essentials 5.5. I will be adding a vCenter appliance for management. Sounds like I can just back up the VMs (just to be prudent) and upgrade each of the standalone hosts to 5.5, re-add the VMs and install the vCenter VM and I should be good to go.
Thank you.