Whilst living in Bielefeld , I used to go to a bar just around the corner ,supposedly once owned by Hamish Imlach (who was very popular in Germany ) ; there were often German musicians in there playing Irish music ,and they all seemed to be extremely proficient , but never laughed or smiled !!
Also, regarding the Nazis and wartime music ; I went to the Uni in Bielefeld to see a film about young men listening to banned music , ie Glenn Miller etc ; I think it was called "Swing Heil" or something ---it was most enjoyable , anyway !