Let's say I'm taking an international flight with a layover in Dublin, which as a *A lounge. I'm Platinum on US Air so I have Star Gold card... but the international flight I have that day is Aer Lingus, which isn't *A. Do I still get lounge access?
You failed to mention who issued your ticket and what class of service you're traveling. Since EI code shares with all three alliances, IME, I've been able to access *A lounges if it's a UA ticket operated by EI.
Suspended
No. Most *A lounges are departure-only and you must be on *A metal. So no lounge access.
Ticket would be issued by Air Lingus (unless anyone can recommend how to get it issued by a *A airline, which I'd love!)