Savage translates "Ubermech" for J'onn as "superior man"; its literal translation in German happens to be "superman".
In addition to the speaking appearances of the DC World War II characters including Steve Trevor, Sergeant Rock and Easy Company (Bulldozer, Wildman & Ice Cream Soldier) and The Blackhawks, there are more subtle references. The Suicide Squad make an appearance, for instance, and one of the wounded at a medical station has his head completely wrapped in bandages, the visual trademark of the DC Comics World War II spy character The Unknown Soldier.
One of the henchmen mention that "Stryker" is working on the project. This is a possible in-joke about "Sergeant Stryker's Death Squad," an Atlas Comics World War II comic which made it out under the Savage Combat Tales line.
At one point Superman destroys an attacking German fighter by flying through it. Just after this Superman can be seen flying while on fire - a tribute to the Original Human Torch from Marvel Comics who was also portrayed as fighting against the Nazis in the 1940s.
During one of the attacks by the roller wheels, an Army sergeant is knocked backwards by an explosion and clutches his wounded eye. This is meant to be a subtle nod to Nick Fury, who lost his eye and gained his infamous patch in the same manner.