Yes, it is used.
TestMonkey likes external formats, so is not entirely objective anyway nor does need to.

Not to your users (for those you provide), but to the guests themselves: the rss result for guests shouldn't be the login form... It's clear why that is, the forum first checks for
// If guest access is disallowed, a guest is kicked out... politely. :P
elseif (empty($modSettings['allow_guestAccess']) && $user_info['is_guest'] && (!isset($_GET['action']) || !in_array($_GET['action'], array('coppa', 'login', 'login2', 'register', 'register2', 'reminder', 'activate', 'help', 'mailq', 'verificationcode', 'openidreturn'))))
{
$this->_file_name = $sourcedir . '/Subs-Auth.php';
$this->_function_name = 'KickGuest';
}
before it even knows the request is for rss this time.
We could add an exception for 'rss' too... provided that it doesn't display anything for guests in this case.