In a stroke of bad luck (or misplaced good luck), I finally ended up with silk touch, but on a shovel.
According to this article: Which blocks require the Silk Touch enchantment, or benefit from it?, there's lots of things you can do with a silk touch pickaxe, including getting grass and mycellium, which silk touch shovels should obviously be able to do to.
Under normal circumstances though, breaking an ore with a shovel (or anything other than a pickaxe) will yield nothing. Are silk touch enchanted tools a special exception to this - or can I likewise expect not to be able to use my enchanted shovel for any of that good stuff?