I had Hodgkins disease, twice, 20 years ago, and squamous cell carcinoma, 3.5 years ago. Not the same as what he is going through, but some similarities. I went through several operations, chemo, radiation, and worked through my treatments. Each person is different and reacts different to the treatments so it's hard to say if he can or can't work. You do have to be carefull to not be around sick people. I once was in the hospital for 10 days taking antibiotics for an infection I got internally. I don't even remember being around anyone sick either. It's just one of the things we have to watch. I don't know if I can help, but feel free to ask what you want, glad to tell about my experiences.
Good luck in treatments, I wish you both the best.