Oh, good. The sick rat will probably get better on his own. I'd say just watch him for a while and make sure that he isn't exhibiting any other signs of infection (ie. wheezing or gurgling sounds, sneezing, sluggishness, an apparent lack of personal hygiene, etc.) Respiratory illnesses are VERY common in rats, but can sometimes result in fatalities. Quarantining him is a good idea though. Also make sure that you check for any of the same symptoms in your other rats.

Now, I know a good deal about rodents, but I'm VERY new to the herp world, haha. As far as feeding the rat in question to your snake, I personally would wait until the discharge clears up just to be on the safe side.

Luckily, my Ball is CB and has been eating thawed frozen mice successfully. I don't think that I could stand raising rats for him; I'd probably end up keeping them ALL as pets and showing up on an episode of "Animal Cops" at some point. Haha. Good luck.