Google’s John Mueller confirmed on Twitter that AMP pages do not require an XML sitemap to be picked up by Google. Simply making use of the rel=amphtml link is all that Google needs to find your AMP pages.
@Kfowler325 @Kfowler325 No need for sitemaps for AMP pages — the rel=amphtml link is enough for us.
— John Mueller (@JohnMu) October 13, 2016