I understand.
In the documentation here:
vCloud Automation Center Documentation
It states, "By default, the vCloud Automation Center Appliance is configured to use an embedded PostgreSQL database. Forhighavailabilityand large-scaledeployments,anexternaldatabase is required."
In the distributed architecture section:
vCloud Automation Center Documentation
they depict that a high availability deployment of the vCloud Automation Center Appliance consists of two or more appliances.
I would take these statements to mean that no, you cannot set up a clustered vACA deployment using the internal postgreSQL and that you are required to use an external postgreSQL instance when you configure the vACA in a redundant deployment.
I haven't tested this in the lab yet but will follow up to this post when i do.