Even though Stan Lee and Jack Kirby knew perfectly well that combat units were segregated during WW II, they didn't care... they threw Gabe Jones in there anyway. The Howlers were a real ethnic stew in any case, including a redheaded Irishman, an Italian, Jew and a Southern boy. I imagine they got the idea for this from postwar movies which often emphasised the different varieties of American fighting together.
But what if they had gone a step further and published SGT FURY AND HIS INTERNATIONAL COMMANDOS? It might look like this...