This might be a dumb question but....

Would oatmeal be considered a grain? One of my kitties stopped having loose stool issues (which he had basically since birth) when I switched him to grain free, but the only grains he had ever had in the different foods that he ate were rice and corn (if that counts). I do not give him any wheat, soy, or gluten either. He has never tried oatmeal. If I had to change his food, would oatmeal be okay?

It is a grain, yes.  Oatmeal may or may not bother your cat.  What food are you thinking of trying so folks can better help you?  Oh, and list a few of the foods that bothered him too, that may help folks better help you as well.