I'm sure you're talking about the no-sugar type, as opposed to the sugary, flavored oatmeal packets. Like other grains, it's a starchy food that can feed candida, but many candida guides have no problem with moderate consumption of whole grains. One prominent alternative med guide (I have to revisit the book store and write down the exact quote and post it here) states that the digestive bowel chemistry behind whole grains is somewhat different than what happens with refined flours, and that the former is much more acceptable to candida folks than the latter. Stevia might make an excellent and healthy sweetener for oatmeal, and possibly that "Xy____" sweetener I haven't familiarized myself with yet.
One thing to keep in mind is that a candida-related "leaky gut" often brings about food allergies, sometimes to glutens ("wheat allergy"). If so, as happened with me, the grains wheat, rye, barley, triticale, and oats should be avoided, and the non-grass family of "grains" buckwheat and millet avoided as well for some folks since their prolamines are similar to wheat protein.