Again, I don't see a _Belt Buckle_ as taking credit for the actions of another, nor is it a part of the uniform.
Now I personally wouldn't wear it, because even if I really really liked the Army and that division for some reason, wearing a belt buckle just wouldn't be my thing. It's like if I really really liked Harley Davidson, but didn't own one, and then me wearing a Harley Davidson belt buckle. It's not "wrong," it just doesn't make a whole lot of sense.
Now if he were in a military uniform with an Airborne patch on it (with no personal affiliation to the unit), then I'd have a problem with it. But wearing an Airborne belt buckle, or an ARMY tee-shirt, or an FBI hat... it's not my style but I try not to judge other people's style either.