Grounding with conduit and cast aluminum weatherproof box
You'll need to make sure your EMT fittings are rated for being threaded into a hub

The thing with weatherproof cast boxes (Bell boxes) is that they have cast-in threaded hubs in them instead of ordinary knockouts, so that water can be kept out reliably.  However, UL historically did not test EMT fittings for use with threaded hubs, only locknuts, and as a result, many of them have a straight thread that won't mate properly with the tapered thread of the hub in all cases.

Fortunately, there are (weatherproof, even) EMT connectors that are rated for threading into hubs; the Bridgeport 290-RTNPT is an example in &frac12;", and it appears your connector was also tested for hub applications based on what the manufacturer is saying.  Note that the Bridgeport version is somewhat longer than a typical compression EMT connector due to having a short pipe nipple, essentially, as part of the fitting, as shown below (photo for illustration only):



Once that's done, you're good to go

Once the EMT has been made up using the correct fittings, though, you'll be good to go when it comes to using it as a grounding path.  Note that I'd probably be using weatherproof push-on couplings (SIMPush&trade;, Mighty-Bite&trade;) or equivalent for joining EMT pieces together; these are the least dependent on workmanship, and couplings are a common source of issues when using EMT as a grounding path.