Potatoes are only considered non-paleo due to the technicality that they were not widely eaten by Neolithic people, but they are generally considered a suitable food for those on a paleo diet as they’re nutrient dense and lack the anti-nutrients that put paleo-dieters off of many other carbohydrate sources. The only potential issue is that they’re a nightshade, but so are many other fruits and vegetables that fall under the paleo umbrella.
Oatmeal, on the other hand, as a grain, is not considered paleo.