Thanks. I'm asking if anyone here actually looked into this before, or maybe can try on their next visit to an airport with a diners club lounge.
The program is detailed on the link above. It looks like Diners Club cardholders simply show their card at any lounge on the list, but there's nothing about Discover card being accepted.
If all one had to do was swipe a Discover card at, e.g., the Air France lounge in Houston or D.C., to get free access, there'd probably be a lot of mentions of it online. Discover certainly doesn't advertise anything like that as being a benefit.