Yep, I have on occasion. Nothing wrong with them as far as nutrition is concerned.
I personally think it's important to remember that in the wild, infirm animals are the top choice for predators. So, while we like to feed the healthiest stock to our snakes, they'll do just fine on the worst we have, too. I don't see a reason to discard a rat that had good weight and health just because it died of a brain embolism, heart attack, stroke, or who knows what else can crop up suddenly.

I'm not saying feed really sick, thin, weak rats off to your snakes, just saying there's no reason to discard a freshly dead rat that seems ok.