I'm pretty sure that they did have the rule some years back, but haven't gotten a rule book from AMA in years.

But to answer the question, do you need a spinner?

I'd say yeah, a beginner "needs" a spinner for a good reason. An electric starter cone fits and holds to a spinner a LOT better and safer. I've seen beginners slip off "naked" props with their starters and break the prop with the starter. And been tickled that the prop broke on the starter and not their hand.