J.B.
Check with his doctor but once the ulcer heals, he may not need to modify his diet. Ulcers are caused by bacteria, not food or acid. My dad had abdominal bleeding due to a post-op medication burning a hole into his digestive tract. It had to be surgically repaired and he thought he would have to modify his diet after and his doctor said that as with ulcers, once an opening heals, it heals. As long as the medication killed that bacteria and he's symptom free, he should be able to eat a regular variety of food.
While my dad was healing from his surgery, he did avoid acidic foods like tomatoes and citrus....ate cereal, soup, sandwiches, my mom's rather bland cooking, meat and potatoes, etc.