Well, by way of two sources (pointing ultimately to the same source), I was reminded of another medieval text which may connect dwarves and spiders, in this case contextually rather than linguistically. Rather than clumsily stuff this into the crowded thread of comments on the previous topic, I decided to write a follow-up post — voici, suivant.
Of what was I reminded? Among his notes to the chapter “Flies and Spiders” in The Annotated Hobbit (rev. ed.), Doug Anderson alludes to the Lacnunga (“Remedies”), a medieval English collection of medicinal and magical remedies, charms, and spells to ward off or cure an assortment of monsters and maladies. The book cited by Anderson, pointed out to him by Kelley Wickham-Crowley, is too late to have influenced Tolkien , but several other editions and discussions of this text were published before The Hobbit. The contents of the book are quite varied and variously written in Old English, Old Irish (or something approximating it), and Latin. Of these, one in particular stands out in the present context: a charm to protect against dwarves.
Actually, the late 10th- or early 11th-century manuscript (British Library MS Harley 585, folio 167) reads “wið weorh man sceal niman […]” , but *weorh is clearly in error for dweorh “dwarf”, as all subsequent editions and discussions, as well as contextual evidence in the Lacnunga itself, agree . For some reason a bit beyond me, Cockayne translates this as “[a]gainst a warty eruption, one must take [...]”; it must be because he didn’t realize the MS was in error, and yet I do not think *weorh is anywhere attested with any meaning at all, “warty” or otherwise. In any case, since then, it has been agreed this is a charm against dwarves (just as there are charms against elves and other sprites and maladies).
As part of the charm’s elaborate procedure, one must sing a rather curious incantation, which begins, hér cóm ingangan inspiderwiht “here came along a spider wight” [i.e., creature; cf. Tolkien’s Barrow-wights]. What the incantation means, exactly, is unclear. According to Walter John Sedgefield, “[t]he incantatory passage is full of obscurities, but the general meaning can be puzzled out [...:] the sense is that the spider is to ride off, using the dwarf-demon as his horse ... as soon as they have ridden away, the wounds begin to cool” . Well, is that all it takes?! ;)
Much more recently, Philip Shaw has written that “[t]he term spiderwiht is one of the best-known cruces of Old English literature, and, indeed, the history of the English language” . If he is not overstating the matter, we can well suppose such a crux would have attracted Tolkien’s attention at some point during his career. We can’t be certain that “spider” was even the intended meaning, and Shaw goes over several possible theories to explain the word (including scribal error). What is clear is that there is no such Old English form, and though the Modern English “spider” is clearly related to OE spinnan “to spin (e.g., a web)”, I know of no one who has conclusively accounted for the word’s appearance as Middle English spinnere, spi(n)þre, spi(n)ther, etc. In his Middle English Dictionary, Stratmann gives as a probable source Middle Low German spinnere, which is as good as anything. But whatever the word was meant to convey, the editions in print before The Hobbit was published say it was “spider”. I can imagine Tolkien reading this and grumbling, “rubbish! there is no such form!”
So, does the charm bring dwarves and spiders together? Maybe. Could the charm have put dwarves and spiders together in Tolkien’s mind, or reinforced a connection already there? Certainly it could have, assuming this is a text he read and a crux he pondered. It could well be that he made notes on this very subject, now locked away somewhere in the bowels of the Bodleian, awaiting the careful and patient attention of a scholar on a mission. Or with a special interest in spiders, dwarves — or both.
 Grattan, J. H. G., and Charles Joseph Singer. Anglo-Saxon Magic and Medicine: Illustrated Specially from the Semi-Pagan Text Lacnunga. London: Oxford Univ. Press, 1952. Cited in The Annotated Hobbit, rev. ed., p. 214n17.
 For the facsimile manuscript of this passage, see Cockayne, Thomas Oswald. Leechdoms, Wortcunning, and Starcraft of Early England Being a Collection of Documents, for the Most Part Never Before Printed, Illustrating the History of Science in This Country Before the Norman Conquest. Volume III. London: Longmans, Green, Reader, and Dyer, 1866, p. 42 (translation on the facing page).
 See, for example, Bosworth and Toller, p. 1192; and Grattan and Singer, p. 160 (and note 12); and others cited in this post.
 Sedgefield, Walter John. An Anglo-Saxon Prose-Book. Manchester: University Press, 1928, p. 419. For his edition of the text of the charm, see p. 358.
 Shaw, Philip A. “The Manuscript Texts of Against a Dwarf.” Writing and Texts in Anglo-Saxon England. Ed. Alexander R. Rumble. Cambridge: D.S. Brewer, 2006, p. 101.