Niemoller did not oppose Hitler's accession to power, but I expect you knew that. However, eight years in Sachsenhausen and Dachau might indicate that he paid for that sin of commission, and his instigation of what became known as the Stuttgarter Schuldbekenntnis after the war indicated his true conversion.
The point of my post was not to compare Catholic to Protestant per se, but was, however, to note that German Protestants did play an active role against Hitler and some did so in high-profile ways.
"Through us infinite wrong was brought over many peoples and countries. That which we often testified to in our communities, we express now in the name of the whole church: We did fight for long years in the name of Jesus Christ against the mentality that found its awful expression in the National Socialist regime of violence; but we accuse ourselves for not standing to our beliefs more courageously, for not praying more faithfully, for not believing more joyously, and for not loving more ardently." -- Stuttgart Declaration of Guilt, 1945
And this from a man who spent eight years in concentration camps.
For their collective disunity in the face of evil, Martin Niemöller along with all other believers in lands occupied by the 3rd Reich were thrown into Satan's sieve to see who was wheat and who was chaff.
The German electorate in 1932 and 1933 was deeply divided. Practicing Catholics wouldn't vote for a Protestant candidate and Practicing Protestants wouldn't vote for a Catholic candidate. Because of their long history of mistreatment, Jews wouldn't vote for either. The end result was Hitler.
We got a glimpse of that here on FR in the runup to the 2012 presidential election with posters making "principled" stands to not vote for a Mormon.