Another significant means by which Thomas’s influence may have impressed itself on Tolkien was by those same, allusive avenues through which so many of Tolkien’s other influences were mediated to him. To quote Peter Candler,
One can only, again, speculate on the influence of a figure like Aquinas on someone like Tolkien, but in any case there is no doubt that some kind of mediated Thomism was certainly in the air Tolkien breathed—delivered, perhaps, through the pipe-bowl. Perhaps the metaphor is apt—Tolkien’s extra-philological influences seem to have been, so to speak, tobacco- or ale-mediated through the conversations in pubs, drawing-rooms, college quarters (not to mention letters) which were so formative on his imagination.
The most well-known of these intellectual gatherings of Tolkien’s was, of course, the Inklings, the informal literary and philosophical group formed around Tolkien, C.S. Lewis, and Charles Williams. It was in this venue that Tolkien, over the years, had the opportunity to read significant portions of his Middle-earth corpus, and whose membership at times included the likes of Gervase Matthews, a Catholic priest from Blackfriars, the Oxford house of the Dominicans (St. Thomas’s order). Probably the Thomist whose influence was most present at these Inkling gatherings, however, even if his person was not, was G.K. Chesterton. The thought and imagination of both Tolkien and Lewis were much indebted to Chesterton, and Tolkien’s essay “On Fairy-Stories,” which explains many of the literary principles behind his own fiction, owes much in particular to the philosophical outlook articulated by Chesterton in “The Ethics of Elfland,” the third chapter of Orthodoxy, an apologetic work that Alison Milbank has demonstrated Tolkien to have read. Whether Tolkien went on to read Chesterton’s later biography of Thomas is unknown, yet the common metaphysical emphases expressed by these two men are too striking to be wholly coincidental. Chesterton’s study of St. Thomas focuses on three main metaphysical theses of the angelic doctor: the goodness of creation contra the doctrine of the Manichees, his philosophical realism, and the primacy of the doctrine of being, all three of which have and a central importance in the literature of Tolkien.
 Candler, “Tolkien or Nietzsche,” 8.
 Caprenter, Inklings, 186. Matthews even seems to make an appearance in Tolkien’s time-travel story and “apocryphal imitation of the Inklings’ Saga Book,” “The Notion Club Papers,” in the character of Dom Jonathan Markison, whose “polymathy” is described as extending “to some very recondite knowledge of Germanic origins” (SD 149, 151). (Matthews, by comparison, was an expert on Byzantine history.)
 Milbank, Chesterton and Tolkien as Theologians, x.
 Dennehy, “Introduction” to Chesterton, St. Thomas Aquinas, in G.K. Chesterton: Collected Works, vol. 2, 414-17.
Lewis certainly knew Aquinas pretty well, but was outspokenly hostile to the Neo-Thomist movement, especially Maritain – he takes swipes at this in private letters and in one of the novels (I think it was the Great Divorce). But he said good things about Gilson, as I recall.
However, Lewis aligned himself mostly with Plato, as contrasted with Aristotle – I think he probably felt more empathy more Platonist philosophers such as Plotinus, St Augustine, Dionysius the Aeropogyte, Boethius.
Tolkien shows signs of having absorbed Aquinas in his reflections on the soul and body in relation to elves and men, published in the later History of Middle Earth volumes.
Charles Williams made use of Platonic Archetypes in his novel Place of the Lion, and reviews Aquinas very respectfully in Descent of the Dove – but I don’t detect any obvious Thomism in his thinking.
I agree with your identification of hints of Gervase Mathews in the Notion Club character: