Tom,
In the Book "Bitterly Divided" by David Williams one of the chapters, I think it is chapter 5 covers the indians in the civil war pretty well. In answer to your Siminole indians, I think for the most part they were able to sit the war out. I don't know if the book might be at your local library, but it is at Barnes and Noble and I found it interesting in that it puts a different perspective on the whole thing and he has many notes to back up his assertions and while I did not check them all out, the ones I did and I checked many, seem to hold up.
Frank