A lot of hubcaps of yesteryear completely blocked all airflow from the outside. Think back to all the metal hubcaps of the 80s. Never any problems with those. 18 wheelers use them and are at a higher risk of brake fade and failure than any car or van.
Unless you are riding the brakes or racing then you are fine.
I accidentally caught my brakes on fire once by leaving the parking brake engaged on my prelude. I went 3 miles before the smoke started.
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