President of Animal Kingdom
Vader and a reconstituted Maul were contemporaries in Rebels.Didn't they have Vader and Maul at the same time in the past? The Jedi Training bad guys aren't "real" anyway, they are Force spirits, manifestations of the trainees fears. So they can have anyone there in theory and be story consistent.
Darth Vader Was Supposed to Kill Darth Maul in Star Wars Rebels Season 2
Dave Filoni revealed that Darth Vader almost ended Darth Maul's life in the Star Wars Rebels Season 2 finale.