Not sure about the VistaJet aircraft, but none of the XOJET aircraft have Jumpseats. And all of their empty legs are advertised to the charter markets. Even if a flight departs empty, it could be diverted mid-flight to a new destination for a number of reasons, leaving the jumpseater high and dry, 100s of miles from where they thought they were going. I once departed SJC for PSP and got turned around to PDX. Reciprocity in an on-demand world isn’t really possible.