Hi,
Yes, Google Apps accounts are supported, but via the standard Google login form. As you mentioned, the limitation is that it's not possible to filter with a specific Google Apps domain. Redirecting to the Google Apps login form does not work.
The initial issue is that the Google discovery process is a bit different with Google Apps domains. It's
badly supported by openid4java, the library that is used by the sonar plugin.
The JIRA issue has been created :
http://jira.codehaus.org/browse/SONARPLUGINS-2034Regards,
Simon