Nope, Disagree Showjumplife. If your running martingale is adjusted CORRECTLY, then it is not in play AT ALL when you have rein contact and your horse is carrying itself correctly. If its adjusted right, it will only come into play when the horse throws it's head up. If your running martingale interferes with the contact while your horse is travelling normally, ITS TOO TIGHT!!!
Also, of course the martingale is not going to directly effect his legs. Duh. But it IS affecting how he can use his body over the jump. He is unable to stretch his neck out over the jump, which in turn means he isn't using his body correctly, which in turn can affect his leg carriage.