Francis Lieber seems to have been a prominent example that the large numbers of German immigrants entering the United States were not friendly to the slavery cause.
My great X5 grandfather immigrated from Germany sometime early in the 18th century (b. 1708, Germany, d. 1749, Lancaster Co. PA). His descendants lived in PA, OH, and IN up until the Civil War but I don't know where any of them stood on slavery, other than they didn't have it where they lived.