If he is confident and able to communicate, I believe that he will be fine. As a doctor, your actual knowledge is obviously very important so if he is strong academically and competent, that should compensate for the stutter. I personally have met three doctors who stuttered. One even went to Harvard Medical School and is now a professor himself at a medical school. The other practices family medicine and successfully runs her own clinic. The last one is a psychologist. All are out there being productive and useful members of the medical community. Ultimately, it will come down to his personality and attitude. Personally, I wouldn’t have made it so I opted for something less stressful and verbal.