This is a technical forum, and license questions goes over the head over most techies.
My assumption is that an SQL Server instance in AWS, GCP or other cloud services that is not Azure, is just like another instance on-prem, and as I recall you can have a passive DB in your AG, both with and without SA. However, for an authoritative answer, you should consult your local Microsoft representative. Or you can call 1-800-426-9400, Monday through Friday, 6:00 A.M. to 6:00 P.M. (Pacific Time) to speak directly to a Microsoft licensing specialist.