Ah, MM Tom Hagen, I learn something new here every day. Was that tidbit in the movie or in the book? I don't remember it being mentioned in the two GF films.

I don't think we saw too much of Rocco in the first GF (at least not a lot of him walking around), so that war injury is entirely plausible -- and it makes more sense than Rocco kicking an armoire in his boss's bedroom.