Holocaust book written by a German soldier?

Not that I know of. In his book "On the Natural History of Destruction", the late German novelist and essayist W.G. Sebald writes about how the whole of German literature is virtually silent on WWII, even though the German civilians suffered some of the most brutal assaults from the Allies, e.g. the bombling of Dresden. From memory, he does list a few German novels that have attempted to discuss these difficult issues. Some of them might make interesting reading for you, but you'll need to get Sebald's book to find that list. I don't have it.