If an independent colony is the same race, can it be used somehow? Is there a way in DWU to incorporate an independent colony into my empire?

Or is the only way to get them as part of the empire to invade and take them over?

This question had allready been asked and answered but...

If you have an independent colony ou can send a colonyship instead of invading, while the colonyship is selected you should get a info if you choose the independent colony..some text that desribes your chance that the colony join your empire.

The chance is based on the attitude between the major race that live on the colony and the race of the colonist, the current relations and the major race of your empire isn't important.