There are many factors involved. Diabetes will affect his SVR rate. But nothing can be done about that. Everyone has factors they can't change that impact SVR rates. Age, race, extent of liver disease, etc. So I really wouldn't worry about it. The bottom line is that with new treatment the chances of successful treatment has never been better. Having not treated before is a big plus factor.
Has he had the IL28B genome allele test? That is "the best" predictor of treatment outcome. Not every doctor uses it as it is a relatively new test but you might want to ask for it.
With diabetes as the only factor the odds are about 71% that he will have successful treatment. (ref. Study 108/ADVANCE SVR Rates By Select Demographics and Baseline Characteristics). There are other factors too that affect success. Race, degree of liver damage, age and many more. The only way to truly know is to try it and see how a person responds to treatment. Everyone is different and their is no crystal ball to guarantee success or failure.
Once he sees how his viral load responders to treatment you will know a lot more.
Best of luck to the both of you!
Hector
interferon ribavirin telaprevir
Which triple therapy?
Hector