Yes, you certainly can use oat flour in cookies! I love that this is one of the gluten free recipes for which I would recommend a single flour. Sorghum pancakes is another one. In most cases, a combination of flours works best in gluten free recipes. You might know that I don't like to recommend a general all-purpose gluten free flour that may not have been tested for a particular recipe. The gluten free flour combination that works best depends on what you're making with it. In this case, oat flour will do the job on its own!