Yahoo take no notice whatsoever of URLs/domain names, despite recent rumours about them only accepting root domains (sign up for my newsletter for more info on this).
When you submit to Yahoo, if you're lucky enough to have subject matter on your site that fits comfortably into more than one category, then the Yahoo! staff will put you into as many categories as they see fit.
For example, when I submitted the "Clearly James Glassblowing" site, I only asked for one category, but got given three. If you look it up, you'll notice that all three categories are closely related.