Apparently, Skyteam members have a lot of discretion as to when they will let you use their lounge. In Jo'burg, for instance, there is no Delta lounge and Air France will only let you use the lounge if you are connecting to a AF flight. Conversely, I've been able to use the Alitalia lounge in Rome even though I was flying Lufthansa, but found that sitting in the terminal amongst the hoi polloi was preferable.