We have two cats and two dogs that live together harmoniously, but they were introduced when they were young. We got the kittens first, and at about 8 months old, we brought home Couver (a 5 month old puppy). Khloe came to live with us around 5 months as well, so she does great with the cats.
I would go meet the cat and see how he and Dex do together. It doesn't hurt to go see
