This story of a dog nursing an orphaned infant squirrel reminds me not only of the recent "adoption" of a baby hippopotamus by a tortoise, but also of an incident some years back with my dog Piccolo.
It was spring, and the grass in back yard was a little long. I let the dogs out for their morning romp, but when I called them back in, Piccolo stayed where she was, lying on the ground. Not even the promise of a dog treat would get her to come. Worried, I went over to her, and found her curled protectively around a nest of baby rabbits in the grass!
I checked the web for rabbit care information, and found out that these were almost certainly not abandoned bunnies - mother rabbits often leave the nest, in order to forage and to distract predators. If you find a nest of baby rabbits, it's best to leave them alone.
I finally got Piccolo to come inside, and kept the dogs away from that part of the yard for the next week or two.