The title World Heroes implies characters who come from all over the world (not unlike many other fighting games). Germany needed representation. Judging from all the Japanese games, cartoons, and comics I have been exposed to, it seems that the idea of the German soldier is popular there. If a character is going to be a German soldier, it makes sense that they look like one.
Let's look at the following characters who could have possibly inspired Brocken:
1. Brocken Jr. (Kinnikuman)
2. Stroheim (JoJo's Bizarre Adventure)
3. The Terminator/Others
Also, each character in the World Heroes series is based off of a historical figure. Although Brocken could represent the idea of the German super-soldier, I believe that he might have been inspired by:
1. Erwin Rommel.
By the way, Brocken Jr. predates Capcom's M. Bison/Vega.