I was using SSO in a HA configuration on my current project. I found it was extremely complex to setup and administer.
Further we had failures in the environment where we were locked out because of the implementation. We switched to a multi-site configuration without HA. So each vCenter server had it's own SSO server, which had it's own SQL database. This worked much better then the previous configuration.
Generically speaking I don't think VMware PSO recommends implementing SSO HA, even though the feature is available.
Cheers,
Paul