First of all, "dashi" simply means "soup stock." As I understand it, what he is avoiding is "sakana no dashi" (fish stock), but he is okay with any other dashi without seafood.
Now, I'm afraid that it's often difficult to sort allergens by names of dishes, because many Japanese chefs or food manufacterers (such as sauce makers) prefer to use fish dashi just to add flavor.
Also, the reason that people suggest things like yakiniku is because it's basically beef heated on a pan. But to seeson that beef, you need seasonings. Some yakiniku dishes may be marinated in fish dashi depending on the chef. Similarly, examples you gave us on your initial post are dishes that were imported to Japan only about a century ago. In other words, it would even be better for you to go to Indian curry resturants instead of that of Japanese curry, or try European cutlet instead of "ton-katsu" (pork cutlet).
It would depend on how serious his allergy is, but one of the best things to do is to book a hotel with a reliable concierge, email in advance so that you know that the person knows what you're talking about, and have all restaurants reserved through him/her. This is what I successfully did when we had allergy problems.
Otherwise, all professionals in Japan concerning food are educated about food allergy, so if you tell them your situation they will mostly understand. Be sure you talk to the manager (tenchou) or the head chef (ryourichou) of the establishment. This is important not only for your safety but for your convenience. Some waiters may have second thoughts about accomodating allergic customers, while chefs and managers usually welcome them as long as they have the right material in their kitchen.
Meanwhile, this "Allergy Sign Plate" saying "I am allergic to..." may be useful. Have the conceirge (or anyone you truly trust) translate/pick what you need. http://www.bousai.go.jp/taisaku/hinanjo/h24_kentoukai/2/pdf/7_5.pdf
Actually, the more authentically the establishment, the easier it is to avoid seafood material. For example, authentic "yudoufu" don't use any type of dashi at all, but just tofu. Many other dishes only use kobu seaweed as dashi which can be easier on him than fish dashi. So if you book in advance while informing about the allegy, chefs can plan ahead to avoid the allergen, meaning most of them can still make Japanese dishes without using fish.
Either way, don't trust anonymous internet users like me if his allergy is serious. This is just to get you started. Bon Appetit!