You may choose to protect VMware vCenter Server using third-party clustering solutions including, but not limited to, MSCS (Microsoft Cluster Services) and VCS (Veritas Cluster Services). VMware does not certify these third party solutions. VMware will provide support for any issues encountered with an environment that uses third party solutions for protecting against VMware vCenter Server downtime. However if your issue is deemed to be related to the third party clustering solution, VMware will refer to our third-party software policy. Source: VMware KB: Supported vCenter Server high availability options