Update Manager is compatible with vCenter Server and vSphere Web Client of the same version.
Update Manager 6.5 is compatible only with vCenter Server 6.5.
During installation you connect the Update Manager 6.5 server to a vCenter Server 6.5 system that runs on Windows OS. After the Update Manager server installation, the Update Manager Web Client 6.5 is automatically enabled on the vSphere Web Client 6.5 that you use to connect to this vCenter Server system.
During installation you cannot connect the Update Manager 6.5 server to a vCenter Server Appliance 6.5. The vCenter Server Appliance runs its own instance of Update Manager as a service.
To see more information about the Update Manager compatibility with vCenter Server and vSphere Web Client, select the Solution Interoperability option from the VMware Product Interoperability Matrixes at http://www.vmware.com/resources/compatibility/sim/interop_matrix.php.