I see this approach as different to RB. Where RB are directly speeding up the airflow by mixing the exhaust into the diffuser, Macca seem to be using the exhaust to create 'air skirts' that effectively widen the diffuser and create a bigger vacuum that also speeds up the air.
Two different approaches with similar outcomes. CFD would be guiding them as to what would be more effective.
We saw some of this last year with some teams, including RB, using deflectors to direct some of the exhaust behind the rear tires.
I believe Renault's FEE are being used as well to create air skirts similar to the rubber skirts of the seventies (Brabham?) that used to run the length of the car.