Solving mysteries: Mewlips and badger-folk. Fiction inside of fiction, or not?

So my question is, what do you think about the creatures seen in poems from Adventrues of Tom Bombadil? Are they part of this world or just a legend of it's inhabitants. Definitely there are mysterious creatures out there which origins are unclear, some are mentioned only few times or once and not elaborated upon enough to characterize them. Sometimes there are whole races in shadow of mystery like Stone Giants, vampires, werewolves and their relation to Wargs, Mouth of Sauron steed ,,mounted upon a black horse, if horse it was; for it was huge and hideous, and its face was a frightful mask, more like a skull then a living head, and in the socket of its eyes and in its nostrils there burned a flame" and countless other creatures hinted to exist the myriads of eyes in Mirkwood hint on some strange monsters, also Old Forest is reputed to be inhabited by queer things could it be that the badger-folk are one of them? What about the sea monsters, ,,dark shapes in the woods" which haunted land of Bree after the heroes departure on quest?