I don't know.
Ash and his friends infrequently meet the members of the Elite Four, who then impart them with battle strategies. So far, Ash has encountered the complete Kanto group:
Lorelei in The Mandarin Island Miss Match (named 'Prima' in the English dub)
Bruno in To Master the Onixpected
Agatha in The Scheme Team
Lance in Talkin' 'Bout an Evolution (mentioned to be the Champion rather than a regular member of the Elite Four)
Ash has also met Koga in The Ninja Poké-Showdown, though merely as Fuchsia City's Gym Leader and not as an Elite Four member.