The effect activates in the Damage Step before flipping the monster face-up. When "Neo-Spacian Grand Mole" attacks a face-down monster, the monsters are returned to the hand without flipping the monster. Flip Effects will not activate.
If "Neo-Spacian Grand Mole" is attacked while face-down, or is otherwise not face-up at the beginning of the Damage Step, then you cannot activate its effect.
These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official and can still be correct, as long as they follow the official gameplay rules, or unless Konami has issued a ruling that says otherwise. References: 
↑Konami Judge Program Rulings are considered unverified, as their source(s) are not publicly viewable. They are not confirmed as applicable to the TCG until they have been officially published by Konami.