There's a good post on this topic by Michael Webster that should clear things up.
http://longwhiteclouds.com/2012/10/22/clustering-support-on-vcloud-director-and-vcenter-databases/
Snip:
vCenter Server – Not Supported, vCenter Server Heartbeat is the supported and recommended solution for database high availability.
There is no explicit support statement from VMware that they have tested and verified the configuration with clustered databases at the time of writing this article. VMware will provide best efforts support and still help customers troubleshoot their environments. But like most vendors if they suspect a problem caused by the clustered database or clustering technology will refer the customer back to the vendor of that technology.