There was some discussion about the swords awhile ago, and I scanned the covers & put them up on Flickr, here:
The Dragonbone Chair spine is here: http://www.flickr.com/photos/strangeshe/3249186786/
Michael Whelan (http://www.michaelwhelan.com/) is the artist for the original edition MST books, and though I am not certain, I would think he also contributed the illustrations for the swords on the book cover spines.
Usually, however, book jacket designs are handled by the publisher's art department -- selection of typeface, layout, etc. So the final art for the book spines -- including the scrolls and other decoration -- was probably handled by someone other than Michael. (Michael is primarily an artist and illustrator, independent of all the various publishers who have commissioned him for covers over the decades.)
However, I will say I could be wrong about the final, full jacket design being handled by a team. ;)
(I'm away from home, otherwise I'd check the actual book for credits. Will try to do later & come back to update here.)
(Incidentally, the illos for the sword hilts that are on my flickr page -- the ones that are different from the jacket art -- were done by someone else, I don't know who. The names given to those illustrations are from whomever is the original artist; I did not name them.)