I flew VIE FRA yesterday on OS in C on short notice. All day flights more or less were fully packed... it seems that both benefit a lot from each other network between LH and OS. Service was good, hot meal even for a 1:10 hour flight!
It would however be strange to have OS in skyteam since CSA would be quite against I presume, as both tend to serve a lot of Eastern European countries. It was the main reason for Malev not to be in Skyteam AFAIR.