Mawalton,
My mom is about 17 months from the end of radiation and has a similar situation exposed jawbone. It only now that it is really starting to heal up and her pain is finally subsiding and she doesn't have to take painkillers anymore. Its been a long rough road but maybe there will be an end to the pain soon for your husband. My moms ENT would not offer her any HBO treatments or anything just let her know that these things take time to heal.
I'm hoping things get better for your husband really soon.
Dani