Hi,
In LabVIEW it is no problem to use more interface to one, in this case, recorder.
For the recorder the Serial interface (C2/C3) is an option. Maybe the recorder can communicate on both interfaces.
With T&M instruments from Yokogawa you have to choose an interface on most (if not all) instruments. So there it is only possible to communicate with one interface.
Just build two simple VI's which will communicate with the recorder, run them both at the same time and see what happens.
Kees