My great grandfather (German from the Sudetenland) fought under the Germans in the WWII at the battle of Vitebsk and, if memory serves, was shot through the leg.
My great great uncle (American) fought under the Americans in WWII as a sniper hunter at Remargen.
I'm told I'm related on my father's side to one of the guys behind MacArthur in that photo of him returning to the Philippines, and that some of my ancestors fought (and died?) for the North in the American Civil War, though I'm fuzzy on the details in both cases.
There have been others, but those are the only ones I know of that definitely saw combat.