Put your vanilla rice dream on the hot cereal before you add the oil and it should be okay. Once you get it into your bowl the temperatures are such that they shouldn't hurt the oil.
Buckwheat is debatable. For most people, it's so far off their immune system's radar that they won't react to it at all. But some people with severe celiac disease react to any kind of gluten proteins. If you don't feel the classic symptoms after eating it (fatigue, elevated heart rate, brain fog), then you're okay.