I would say that dreaming is an altered state of consciousness experienced already through the third eye. Which means that in that state, you're using your third eye. Now if you are conscious enough in the dream to stimulate your third eye, that would in my opinion be a legit way to learn how to stimulate it better while awake because you remember how it felt in the dream and can more easily do that in real life.

It would maybe be compareable to the idea of stimulating you're third eye on cannabis or mushrooms. The altered states give you more access to such practices and it should help your awake practices