You do not get credit from a college if you don’t get admitted there. Nor do you get admitted just because of good grades in a rigorous prep. And some ECs thrown in.
I am absolutely with @helpingmom40 and @momofsenior1. Adcoms like supporting metrics and you never want them asking, why no AP scores? Or, guessing they did not represent well.
The next kids, from his prep or other similar, may be submitting their whole packages, have the same top grades and provide all the supporting numbers.
So, of course taking the test and doing well can help hm get into a selective.
Unless he does get recruited. I wouldn’t bet the whole farm on being a recruit when things can happen. It’s a 3 hour test (and some prep for it,) 8 months from now.