Yes, the barge boards are now used to further seal the entry into the floor area, to prevent dirty air from entering. All this means that most of the air that runs under the car comes from under the driver, which is air coming from different ways around the nose and ends up under the bulkhead. Every car has various turning vanes and aero parts designed to increase suction in this area, so that more air would end up in there.
Barge boards (the vertical bits) are used to suck that low pressure zone outboard, once we reach "the safe zone" (safe from dirty air), then most of it ends up under the floor since we now have big rounded leading edges creating another low pressure zone. Final destination is diffuser of course.
For a while I was surprised that teams put the splitter so low, it didn't make any sense. Until it hit me - maybe they are using it to scoop even that low air next to the ground (no boundary layer on the ground, remember
) since its mostly unused up to that point, it only passes under the centre FIA FW section.