Oats don't make horses hot or nuts... Oats give energy. Lots of it. If that energy is being channelled, then there is no problem, and they are very beneficial.
If, however, the enegry is NOT being channelled, or not enough is being channelled, is when you run into problems. The horse has more energy than he knows what to do with, and may become 'nuts', lol, or hper-active may be a better way to put it.
If you have the knowledge and feed oats correctly, I don't see a problem.