Originally Posted by nickflies

I understand that for the AF lounge at FRA (and broadly for other outstations of DL) but at FRA this one is called the "Sky Lounge" and on the SkyTeam website it says "you can access this lounge if you are an eligible passenger traveling on an international flight operated by the following airlines" one of which is DL.

It doesn't list any type of exception there to the normal ST access rules, whereas the AF lounge is noted as just for AF/KLM/Czech which is fair enough.