Indeed you should get into that lounge with your EK buss.
Otherwise theoretically one should have a Star Gold Card to get into the ROP Lounges.
Recently though I flew on Qatar from Kathmandu and I asked if I could use the Thai ROP lounge (very austere in Nepal!) and got a Yes Sir, although I said I was flying on Qatar (and not code-shared with a * flight.
When I left I asked the attendant if they changed policy. She said no, but that they allowed ROP Gold members unofficially ("because good customer sir!).