This one?
It looks like the dimples recess the fastener and are tapered out to minimize their influence.
An airdam and spoiler can interact with each other (Porsche) and they're on opposite ends of the car. The airdam/diverter, wheelwells, bellypan and diffuser all act together. Airflow is segregated by fences, not dimples. "...the reynolds numbers" is actually
Reynolds number[singular], a dimensionless quantity.