Originally posted by UCanShootMyNovaHe was still Vader's apprentice when he fought Brood. I don't think Galen considered himself otherwise until after Vader betrayed him on Corellia; though I could be mistaken.
He considered himself an apprentice of Vader though I can't remember if he faced Maris before or after thinking about whether to betray Vader and use the Rebel Alliance as his own tool.