This is a difficult question to answer without knowing the full clinical picture. What is his day to day ventilation settings? Just because he is down to 30% doesn't meet his PEEP is down. How has his spontaneous breathing trials go? What does his CXR show? What do you mean the blood work is great? What are his I/Os? How is his kidney function?
When you sign a DNR it isnt just a genetic DNR. There are different sections to it. It asks if you are ok being on a vent if needed. It asks if you are ok having a feeding tube if needed.You can be ok with life support, just not CPR if it comes down to it.