Out of the five little dogs I have had over the years, all but two has made all kinds of sounds while asleep. All the hyper ones seem to do it. Some even yipped, don't think any barked.
I do have a 16 year old cat that will 'talk' if he runs out of water or wants out of the room. Sounds like he is trying to say hello with out the Ls. He makes other noises also. He is wide awake.