I have not heard if anyone being "detained"while connecting on separate tickets. You will be escorted to transit security like everyone else that's connecting, just make sure to have a print of your e-ticket, if you can do online check-in with EK and get a boarding pass even better. I don't know if EK issues OLCI boarding passes, most airlines don't due to document checks.

Currently, everything airside apart from the vending machines close around 7pm.i have taken the QR flight several times, once the JL lounge was open until departure, but that was right after the Olympics ended, and the airport was rather busy with flights. But if there is no JAL departure to Hawaii that day, count on the lounge to close after the US mainland departures.