It's a little difficult, based on your description, to tell what sort of weed this is, but yes, it is a weed. Corn gluten, and any other weed preventer for that matter, doesn't offer perfect control, and doesn't affect all weed species. You can take a sample in to a master gardener or extension office for an ID. Then you can definitely find out, by looking on the package labels, which weed preventers will work on it.
As for natural controls, corn gluten is about it for weed preventers. If the weeds are perennial and come back every spring, you'll have to remove them by hand if the corn gluten isn't working. Meanwhile, mow your lawn high and keep it thick and healthy, which will help it compete better with weeds.