As others have indicated, the OP won't have an issue boarding at Meidling.
Originally Posted by
the810
Besides, conductors pretty much never check tickets between Hauptbahnhof and Meidling, it's a too short distance and they'd have to "recheck" the carriage again anyway for the new people who boarded at Meidling.
Agreed that it's unlikely on an OeBB Railjet. But a couple of times, in first class on an DB ICE leaving Hauptbahnhof, I've had my ticket checked before Meidling. The conductor then stands at the forward door for departure from Meidling and it's fairly easy for him to see who boards in first class before passing through to check tickets in second class.