Well in general variety is key, and adding different canned foods is one way of obtaining that. Canned foods also tend to hold more meat content, so I'd say it's definately in the benefit of the dog to add some.
They can also stick to evo, and rotate the different formulas, and that's still sticking with the same brand, but giving more variety.
In short: yes, adding a variety of cans is a good idea to a kibble diet, especially if there's no rotation going on.
BUT, canned foods are more expensive than just adding normal meat.
ETA: it's debatable. I think yes because canned foods generally have more meat content and are therefore closer to a dog's natural diet, they also hold more moisture, obviously. In the wild, dogs get a good amount of their moisture from the food they eat, not from drinking water. (this applies even moreso to cats)
Some argue that an all canned diet is bad for teeth, but I think kibble's "teeth cleaning benefits" is one of the bigger kibble myths. It's kibble that gets the gunk on the teeth to begin with. Try eating coco pufs for a week without brushing, and see how much it cleans your teeth. lol