The PDF file downloaded from Server to Data Center: The Tipping Point states on page 28 that:
In Data Center, it is required that the database be installed on its own node. If you so choose, clustered database technology is supported and recommended as it provides further resiliency to your system; although, a clustered database is not required. Data Center supports the same databases as our server offering but be sure to consult the supported platforms page to ensure that your preferred database technology and version are supported.
This ticket and JIRA's Supported Platforms should be updated accordingly to be in line with that. It's not clear whether database clustering is officially supported for Data Center only and, if yes, starting from which version.