During the whole course of the show (with the exception of one or two episodes) All the German soldiers are shown using 9mm Lugers, but in fact near the beginning of the Second World War Germany changed it's standard sidearm to the Wather P38. So all the Germans have the wrong gun.
Although the German Military began to produce the Walther P-38 to replace the Luger P-08, the Luger was never officially removed from service, due to the massive quanities of Lugers still in service. It would be very difficult for the Germans to round up all of the old P-08's anyway, so many remained in the hands of German soldiers until the wars end.
There is nothing wrong with the pistols used, but, and this is a big but!
The German guards are repeatedly shown to be holding American Thompson Submachine Guns, also known as the "Tommy" Gun. Furthermore, the models they hold are not even the ones used by the US Military in WWII, but rather earlier models from the 1920's. Not that it makes much of a difference, considering the size of the blooper.