Yes, this DNN stuff is real and not just marketing because it has existed in 3 generations of Oticon aids, from the More and Real with the DNN 1.0 to the Real with the DNN 2.0. Many people have reported better speech in noise performance in the Intent and the same between the More and Real, so it's consistent with the DNN train of progress.
How do you determine if it's actually working and makes a difference? Well, Oticon aids have been selling very well from since the OPN in 2016 until now, so it must be working because just fake marketing nonsense will not sell itself through 5 generations of aids by now (OPN, OPN S, More, Real, and Intent). The Intent has been very well received based on forum feedbacks, specifically on making a difference in speech in noise for people. But individual mileage varies so there's no guarantee that it'll work for you personally even if it works for many others. You just gotta try it out for yourself to see.
As for commenting on the Intent DNN, that's such an open question to deserve a good answer. I guess my comment would be that the Intent DNN is as real and as effective as one can judge based on the positive feedback of audiologists (see Dr Cliff's YouTube video) and actual users alike (read up on the forum users' comments yourself).