For all of the non-socialist and communist parties however, it didn't matter what ideology they were, because voting for them wouldn't result in that. It'd result in Hitler and the Nazis.
One could argue that every vote for the Zentrum is a vote less for the NSDAP. Had the Zentrum received 33.1% and the NSDAP just 11.9% of the vote in the last fully free Reichstag election (instead of the exact opposite, like in real history) it´s doubtful that Hitler would have been appointed Chancellor in the first place. No Hitler, no "Enabling Act".
To play it safe though, I would still urge to vote for the SPD.