I have worked with German re-enactors, of both wars and all nationalities. As I come from Jersey, which unlike England was Occupied by the German's from 1940 till May 9th 1945, most of my teachers and the adults who influenced my childhood lived there during the Occupation, always spelt with capital letter. I didn't learn about Nazi atrocities from history books , I learnt from the people who experienced it . My playground was the bunkers. It is still a very sore point on the Island, and in some parts of Europe. However that said, It is only by presenting all sides of a conflict that the truth gets a chance. A lot of Jersey people had a respect for the Wermacht troops as individuals. It was the Organisation Todt that was held in the greatest contempt. To be exact the Gestapo was never present in the Islands, it was the Secret Field police, mind you if you ended up in their hands for say riding 2 abreast on a bicycle, then the difference was academic. British Civilians did end up in the concentration camps, 12 did not return.
The important part for anyone wearing uniform at a show is tolerance . Sooner or later someone will get upset or ask an awkward question, think before you reply.