Do you mean greenfeed (ie: allowing the oats to head out, then cutting it in the dough stage) or cutting it when its still in the leaf stage, just before heading out? We've fed greenfeed here for years and never had a case of bloat out it. Its one of the popular ways to feed cattle up here, as you can get several ton an acre out of a cut, and not have alot of inputs in.
Never cut oats in the grass stage, so I can't help you there, but I find it unlikely that it would be any hotter than any other lush grass, which is to say, not very.