I don't know why the NCAA regulates how coaches get paid. Put a cap on the number of total coaches, fine. But to say that only two can be paid is ridiculous.
That being said, I don't know if it is completely necessary to pay a third assistant. Either way, they're doing alright. Went to a camp last year at a Big 10 school. $350 dollars for the two day camp. 150 kids there. If they hold two of these camps a year and are only taking away the cost to produce t-shirts then they're walking away with a nice check.