That is correct. Carl Schurz being one of the most notable examples. Protestent German Americans tended to be strongly anti-slavery, seeing parallels between the Germany monarchical oppression they had fled and the oppression of blacks in the South. Which probably loops back on the question of why Know-Nothings disliked German Protestants.
The Republican Party was such an amalgamation of factions they had both Northern Know-Nothings as well as anti-slavery Protest German immigrants. Edward Bates had some involvement with the Know-Nothings and that made him seen as liability for the Republicans. One of the big reasons Lincoln got the nomination is he didn't have any of the baggage the three contenders ahead of him had (see Doris Keane Goodwin's A Team of Rivals, among others).
Schurz was baptized a Catholic and received a Catholic education as a child. Schurz remembered his village as having only one Jew and no Protestants, it was so Catholic. In later life, Schurz was more an exemplar of the secular German.
Some Protestant Germans were strongly anti-slavery, but Lutherans were often described as being similar to many German Catholics who were quiescent on the issue of slavery.
Bates was not the only Republican to be tainted with Know Nothing affiliations. Thad Stevens, Henry Winter Davis, U.S. Grant, Nathaniel Banks and many other had ties ranging from deep (Davis, Banks) to brief (Grant, Stevens). Republican Know Nothingism reappeared in the mid-1870s.