Personally, I think that dogs enjoy some variety. I think dry kibble day after day is totally boring and doesn't give a dog much enjoyment. I am always mixing in something and a good canned food is no problem, in my experience. Mix it in with water so it can't be picked off the top. So, I say go for it.
I don't think dry kibble has anything to do with having dirty teeth. My evidence comes from taking care of 20 dogs over a 12 year period where they were all fed pretty much the same thing -- a basic diet of kibble -- sometimes dry, sometimes with water and sometimes with some canned food or other meat, etc mixed in. They would get a raw, meaty bone every once in a while.
Some of the dogs never needed to have their teeth cleaned. Others, fed and taken care of pretty much the same -- needed theirs cleaned every 6 months; others, maybe every 2 years. To me, it seemed to have nothing to do with what they ate. I think it has more to do with the quality of the teeth -- hardness of enamel and perhaps the quality of the saliva.