And the answer is yes. There is a sign outside the lounge that lists the ways in (much like the web page link I provided above, except it lists *Gold as able to bring a guest). Showed my BP and Altitude card to the agent at the desk. She looked somewhat strangely at the card for a few seconds, and eventually asked me if it was a gold card. I pointed put the *Gold logo and she said ok And handed it back to me.

Very nice lounge, by the way! And not at all busy.