No, they never did. It seems obvious to me that the thought process was

  1. Humans are being enslaved by psychic powers
  2. There's multiple different alien races in the war with very different environmental requirements
  3. What if some of those alien races were also enslaved by psychic powers
  4. Humans figured out how to break psychic enslavement
  5. Therefore, it makes sense that the humans could free some aliens
  6. Grateful aliens would fight with the humans to not be enslaved again

This works at two levels, too: it explains the presence of wildly different creatures created for gameplay reasons, and as a world-building exercise it’s more probable that when the evil empire shows up it’s not the first time they’re trying their playbook.