You didn't say which low carb plan you're following. The Zone recommends slow cooked oatmeal several times a week. (But that's not really a low-carb plan). This is because oatmeal apparently has essential nutrients that aren't easily found in other foods. But as far as I know, Atkins, PP, and other plans that don't factor in the glycemic index do not suggest eating oatmeal.

However, because I'm avoiding soy, I eat slow cooked oatmeal twice a week. Portion size, about 2/3 of a cup. I haven't noticed any bad effects on weight. But it does have a lot of carbs--about 14 net carbs per serving of that size. So I'd say, if you can afford the carbs, it's a good food to have occasionally.

And BTW, slow cooked oatmeal takes about half an hour to cook. The stuff you saw is probably the "quick cook" oatmeal. ("Instant" reconstitutes almost immediately).