The Google Apps Login plugin simply logs you in to your WordPress account, using Google sign-on instead of your WordPress username/password. There is no extra option to ‘restrict pages to Google Apps logins only’ beyond any existing WordPress functionality that restricts pages to logged-in users only.
So the plugin should not affect your RSS feed if it was working fine before enabling the plugin.
As with everything related to WordPress, it is possible your configuration or other plugins changes behavior, so in this case the best advice is simply to activate the plugin, and then check that the RSS URL is still visible from a different browser where you are not logged into WordPress at all.
Hope this helps.
Thanks,
Dan
