Tomorrow, I would take a flashlight or head lamp, and look inside his beak and throat for any yellowish patches or things that should not be there. Looking at another chicken first while someone holds it's head for you will help to know what to look for. There are a couple of diseases that can cause plaques or infection in the throat. You won't be amble to go past his tracheal opening, but that is enough.
Did you find out what your roo was sick with? I found your post because my rooster is hoarse right now and I'm desperately trying to figure out what's wrong with him. I'm starting to get scared because so far this is the 2nd post I've read and both roos died