I used the OP's assumption to gain access to the Quantas Lounge in SYD. I was not on an international INT but, juts a hop from SYD to Cairns. I am AA Plat and used UA to go to SYD. I had no problem. I have never tried it domestically.

I suspect the result would be different as some lounges (read the numerous threads about BA's MIA lounge) have difficulty with admitance even if you meet the International reqt.