EKM, that is an excellent post. When instructing on USMC ranges that is the same exact trick I would pull on the young Marine that swore he was not flintching I have seen guys actually have to take a step forward cause they jerked so much, I used dummy rounds mixed in with live just like you quoted.
Any gun in general manufactured in the past 30 or 40 years is most likely safe to dry fire regularly, but why take the chance? For a couple of bucks you can have piece of mind. It is still the opinion of some that the shock of the firing pin going completely forward without striking a primer is still not ideal for the weapon. That being said, the Marine's also dry fire extensively with the m-16, I have never seen one break a firing pin. It has been a while I can not remember, I believe we did not dry fire the 1911 .45, but may have the Beretta 9mm when phased in (maybe there is a younger Marine out there that knows).

"Not as lean, not as mean, but still a Marine"