This is another case of the law of unintended consequences. And as such, is certain to have a brewers exemption. I'd have to imagine that the spent grains have to be about as good and risk free a foodstuff as you can get for animals.
Which is to say that it wasn't intended to screw up things for brewers, it was intended to keep melamine out of your dog or cat's food or baby's formula, Or spinal flud from animals infected with spongiform encephalopathy diseases out of your food or other animals food. That kind of stuff.
Hard to imagine people thinking it's government over reach to keep those things out of the food chain.
So this is just how the process works. Laws are proposed, and people review them. Then if there was a bad unintended consequence, exemptions are made.
As an example, Texting while driving laws are often proposed in various state legislatures. As initially written, they often end up including trained operators, such as police, railroad engineers, and Amateur radio operators. So every time that happens, during the comment period the affected groups suggest changes, which are always made.