It appears that there is one additional setting that is needed to force IBM Connections 6.0 to use TLSv1.2. In each Application Server go to
Process Definiition > Java Virtual Machine and add the following setting in the Generic JVM arguments:
Save the changes and after applying to all application servers, restart the servers.
Note: IBM Technote that this post was originally based on (and I referenced) is no longer available, but it appears to have been added to the HCL documentation for Connections 6.0 CR6