Non-BC/YC guests are not allowed in SAB, they actually scan your magic band on entry to the pool areas. Even pre-Covid when any Disney resort guest could book cabanas at GF and CR, Stormalong Bay was an exception and cabanas there could only be booked by BC/YC guests. Only way I could see them allowing this is if you add the guest to your room for the day, but I'm not sure. SAB has always been much stricter than other pools.
To reserve a cabana, please call (407) WDW-PLAY or (407) 939-7529. Private dining is also available at an additional cost. Guests under age 18 must have parent or guardian permission to call.”