Scanner was finally made to work.
It turns out that the scanner was "almost" working. It was starting the scan and then aborting about 75% of the way through the scan. Later, I also noticed that the preview function would capture some of the image. So the scanner was definitely communicating with Xsane but something was stopping it from completing its scan.
The solution, which I found by pure chance, is to enable "advanced options" on Xsane's "view" menu and then set the bottom-right-y setting to 27.920 cm (11 inches). The original setting was a lot higher than that. Xsane thinks that the scanner is a flatbed scanner whereas the scanner is really a feedthrough scanner. Consequently, any mismatch of actual and expected page width or length, including a document jam, will cause a read error. Further, trying to scan something smaller than 8.5 by 11 inches will also cause a read error unless an 8.5 by 11 inch backing sheet is put behind the document.
Now, the scanner works just fine.