If an attacking unit like Stellacorn Herder that has a move trigger gets stunned, does the controller draw a card if Herder does not die in combat and returns to base?

No, you do not draw a card in that scenario.

According to RiftJudge FAQ #10124, which specifically addresses the interaction of Stellacorn Herder with recall effects:

1. Recall vs. Move: A "Recall" (the mechanic that moves a unit back to the base after it is stunned or fails to conquer) is distinct from a "Move" action. As defined in the game rules, a recall is not a move.
2. Trigger Condition: Your Stellacorn Herder's ability ("When I move, draw 1") specifically triggers only upon a Move action. Because the unit is being recalled to the base after combat, the trigger condition is never met.

This distinction is consistently applied in Riftbound: any ability triggered by a "move" will not fire when a unit is recalled to its base.