I'm the same as Live; I can't eat cereal at all, and if I add fruit as I like it, it spikes me horribly. I eat eggs for breakfast. But if you are asking if you subtract the fiber carbs, yes, if it is more than 5 you can subtract them. But my experience is even if I bolus for the carbs listed I still go high.
Oh boy, Cereal can be quite difficult for a diabetic. To answer your question, you should be paying close attention to the number of carbs, in total, in your cereal. Cereals like bran have a higher fiber content, which may make your "net carbs" lower, because the fiber makes the carbs take longer to break down. I have had type 1 diabetes since age 14, and in general I try to stay away from cereal. Its perfectly fine in small servings, and of course without the added sugar, but its packed with complex carbs which almost always cause a high BGL, at least for me. Remember that rasberries and blackberries are two of the lowest sugar fruits, which are great in bran flakes with skim milk!