As pointed out by Simão, the unit information is not supplied to polkit by systemd on RHEL 7. One way around the problem is to use pkexec to wrap the call to systemctl. You would need a wrapper script for your specific service, then have the rules apply to pkexec. The users would execute the command

pkexec /path/to/script

and the polkit rule would look something like this:

  polkit.addRule( 
  function(action,subject)
  {
    if ( (action.id == "org.freedesktop.policykit.exec") &&
         (action.lookup("user") == "root") &&
         (action.lookup("program") == "/path/to/script") &&
         (subject.isInGroup("someGroup") ) )
      return polkit.Result.YES;

    return polkit.Result.NOT_HANDLED;
  }
);

In a practical sense, this just re-creates sudo and scripts using the polkit framework. Whether this is "better" than using sudo is a value judgement I'll leave to others.