World War II was a landmark in human history, and one that will leave an imprint on German politics for a long time into the future. Nazism and far right politics are taken very seriously there, so it only makes sense that German advertisers would want to distance themselves from these groups to avoid damaging their image.
No, the Germans pulling advertising from Brietbart is not a reaction to the Third Reich. Rather, the Germans are upset that Trump won the election. Trump made it clear that he was not going to continue the policies of the current administration. The Germans don't like this, so they are finding someone to blame.
German firms are pulling their advertising from Breitbart due to the extreme one sided nature of the CEO. These German firms do not want to be seen as far right leaning companies, they want to keep their image as open and tolerant to the public. They want to show they are moving forward and not transgressing into the closed mindedness of the past.
German Advertisers are not acting out of some noble reason to pull ads from Breitbart. They are pulling ads to preserve profits. Right or wrong, Breitbart has been accused of fomenting racist and anti-semitic stories. German advertisers are obviously sensitive to anything that may appear to be anti-semitic, but the reason for pulling their ads from Breitbart is for profit. If the potential problems with maintaining ads on Breitbart were outweighed by the profits, they would continue to run their ads.