The original vCenter Server 5.5 Availability Guide was published in December 2014.
With the End of Availability of vCenter Server Heartbeat guidance was provided on how to monitor and protect vCenter. Due to the need for additional protection, we have internally validated using Windows Server Failover Clustering for protection of vCenter services. Improved SLAs can be attained with this clustering solution. The update provides step-by-step guidance to deploy this solution to protect vCenter 5.5
You can download the updated paper here: https://www.vmware.com/resources/techresources/10444