Looking at test pics where teams map pressure outside the front wheels, that may well be true. The whole vented axle, silver duct and wheel lip seem to interact with airflow coming off the endplates.
Slightly offtopic, I suspect the long silver tube and its shape has an aerodynamic purpose as well. Otherwise, why would they bother routing cooling air above and around the whole brake? They could just route it *under* the disc.
This is especially true of the rear, where the calipers are mounted at the bottom. Yet they route the tube round the back, bending forward and then into the caliper.