Cockapoo dogs and Labradors can have puppies together, with the result being a mixed breed. Since all breeds of domesticated dog are of the same species, there are no biological barriers to these animals producing puppies together.
When two animals of different species mate together, the result is rarely offspring. Only very closely related species can reproduce, and even then, the offspring are often sterile. Such is the case with mules, the result of a horse and a donkey mating.
However, both Cockapoos and Labradors are members of the same species. They may look very different, but in terms of their reproductive system, the two animals are identical. Both are domesticated canines. In fact, the Cockapoo itself is a hybrid breed, the result of a Cocker Spaniel mating with a poodle. The offspring of a Cockapoo and a Labrador would thus be a Cocker Spaniel, poodle and Labrador mix.