My legal opinion is that the statement would have limited effect--almost useless--as a defense, although PI is not an area I practiced in.

And can anyone point to a case where an official was actually sued for failing to identify something in a player's equipment? (That dangerous white elbow sleeve, perhaps?)

If the referee is supposed to inspect, being told they comply does nothing; if the referee is not supposed to inspect, it's hard to point at the referee rather than the coach (and thereby the school) that had responsibility to ensure compliance. In practical terms, referees are supposed to identify dangerous equipment and could potentially be on the hook--but the requirement that the coach certify means, at a minimum, the coach would also be a defendant, as well as the school that employees him.

But I don't think this has anything whatsoever to do with legal liability. It's trying to make coaches responsible for their teams. (In soccer, any cautions for improper equipment would be player issues, except in NFHS where the coach certifies, and then he gets the caution if a player has improper equipment. [For those who don't know soccer, a caution with a yellow card is a rough equivalent of a T in hoops,])