You did mention this was a machine shop....

I like to have a ground wire for my feeders between panels. If nothing else, I really don't like to rely upon the pipe to provide an adequate path for anyhing over, say, 50 amps.

While using the EMT as ground may be legal, one thing that is of increasing concern these days is "power quality." A modern machine shop has much equipment that not only relies upon electronic controls, but also the frequency drives to produce all sorts of transients. I believe that having an additional ground wire, oversize neutrals, and avoiding multi-wire circuits are important steps in ensuring a "clean" electrical supply.