So long as the lounge is in the departure pier that you are leaving in, it matters not the airline. A limited # of lounges require that you paid for your ticket with a DC, but no one has ever checked. I have never visited with a guest so I don't know how strictly they enforce charging for the guest. They simply take your card info down when you enter. Your annual statement from DC will remind you of the opulent benefits you received for lounge use, and when you call to cancel your card, they will also remind you of all the lounge use you received and why would you want to cancel?

I have visited a few of them and they are fine, but nothing extra special.