Aiwendil - Art as it is forms a part of Nature. After all, the Nature itself is created = act of art. Art rightfully employed = sub creation = imitation of the first Act of Art. Only
perverted art, one not conforming to natural pattern, is opposed to Nature.
Besides, it may be argued that only humans when dead leave Nature behind, as they leave the Circles of the World. All else, including ghost world of wraiths, is inside it, though on different plane. Hence, only
Supernatural acts (=miracles) are those coming outside of it - i.e. interventions of Eru - Numenor case, resurrection of Gandalf, and the case of Bilbo finding the Ring. Even in those cases, pattern is natural - the island is overflowed, the body is not destroyed, the finding of the ring is, well, just
chance-finding.
Dratted lack of time, so I must refer you to, instead of developing it on the spot:
Evil Things
Acceptance of Mythology
Those do not deal directly with the issue in hand, but touch upon it as well
cheers