Conduit is a very good ground when installed correctly and when continuity is maintained (better than the ground wire). This does not mean, as an engineer, I allow the equipment grounding conductor to be omitted (I prefer belt & suspenders, or to put it another way: "there is not compromise when it comes to safety" and your systems will be less prone to noise and interference). I prefer compression couplings for conduit and typically do not allow screw type, but it would certainly depend on the application and if you are wiring a motor or say some sensitive electronic equipment. For a very specific industry reference, you can quote: "EPRI's Power Quality for Electrical Contractors, Applications Guide, Volume 2: Recommended Practices, 1994", it states, "The quality of joints is critical for all conduit and raceway, especially for EMT where compression fittings are recommended over set-screw type."