I went hkg-bkk a few days ago and I was able to use the Korean Air lounge via CO Plat card. The agent did not seem to mind that my next flight was EK, but it is probably entirely subjective. Just be aware it is a trek from KE to EK. In terms of other recognition, EK could seem to care less about CO.

Oh whoops Gold, I guess not. This is a reference for any plat!