The North American frontier provides some Native American examples that might apply. Strictly speaking, it may not meet the definition of UW but there are many examples of Native Americans in U.S. service with U.S. advisors.

Here's a couple: the Pawnee Battalion under Frank North; the Apache Scouts under Al Sieber and Tom Horn.

http://www.nebraskasocialstudies.org/notable/north.html

http://www.geocities.com/~zybt/sieber.htm