Douglas Anderson notes in his annotation to The Hobbit that the dwarf names come (directly or by rhyming with something direct) from the Old Norse poem “Voluspá”, part of the Poetic Edda. Anderson includes the relevant passage from the poem and short discussion.
My own theory on why Tolkien chose these names is quite simple: when one is telling the children an exciting story, one uses the first names to spring into mind, like Dasher and Dancer and Prancer and Vixen. So much the better if they rhyme. Ask my kids sometime about the adventures of Mrs. Oliphaunt, a royal elephant in India, and her friends Niobe, Marissa, and Louise. Backward alphabet to the rescue.
Tolkien, J.R.R. The Annotated Hobbit. Revised and expanded edition annotated by Douglas A. Anderson. Houghton Mifflin Company. Boston. Print.