Is airflow deflected inwards or outwards by wing sweep?
As a partial answer following up on those to date, here is an image from Where is the spanwise flow? How does the span wise flow point the air towards the wingtip?, showing a snaking in-then-out flow over the wing. Note the inward flow over the leading edge and wing section, which is just the point where wing fences are located.



On sharply-swept deltas which sit inside the bow shock cone at supersonic speeds, 1980s studies of supercritical attached flows show the air flowing upwards round the leading edge and forming a crossflow to meet an inboard "crossflow shock". See for example W.H. Mason, “A Wing Concept for Supersonic Maneuvering,” NASA CR 3763, December 1983. But it is less clear to me whether this inbound crossflow is physical, or a theoretical notion along the wing profile which, due to the sharply tapering chord with span, physically might still flow outwards:



This contrasts with the low-speed vortex flow over such wings (e.g. Concorde) at high angles of attack, where the vortex inflow is detached and the boundary layer flows outwards.

So it seems the full the answer must be complicated, with the pressure distribution along the chord, and hence the in-out flow changes, depending on the angle of sweep, the speed of flight, the angle of attack and how far above the wing you are considering.