There seems to be some confusion as to whether or not the Identity Appliance that ships as part of vRealize Automation (previously known as vCloud Automation Center, which will be referred to as vCAC 6 for the rest of this article) is required when deploying vCAC 6.1 in conjunction with vSphere 5.5 and later.
As of vSphere 5.1, Single Sign-On (SSO) is a pre-requisite to installing the components for and including vCenter Server. It’s no secret that VMware’s initial implementation of SSO in vSphere 5.1 was terrible. It was over complicated in terms of its implementation requirements, even requiring its own database, to be manually set up using SQL scripts. Thankfully, VMware addressed many if not all of the SSO issues in its release vSphere 5.5, with SSO now being a much more simple and robust component in your vSphere 5.5 environment.