I just finished reading a fascinating book on this subject. The British actually did use Indian slave labor. There's a vast literature on the destabilizing effect of this throughout the Southeast, where a civilization built upon maize agriculture and mound-focused societies transformed into one that valued furs, European firearms, and pre-emptive enslaving of one's neighbors for sale to the British before the same happened to you.

These conflicts between native polities decimated the pool of potential native slaves, and the increasing supply of African slave labor shipped to North America brought an end to this native slave trade in the mid 1700's.

EDIT: I'm never clear on when to use "Indian" and native. More and more scholars seem to be re-deploying the term "Indian" perhaps because of its historical usage, while I've had a few non-academics, all very intelligent people, insist on the more politically correct "Native American". The fun never ends...