The good news is that traditional Thai food is freshly prepared with lots of dishes based on fish and shellfish, fresh green vegetables and a tradition of raw vegetable garnishes. Challenge will be that rice and/or noodles are ubiquitous with Thai meals - if you have enough willpower to limit rice intake to a tablespoon or so, this will help. Thai curries and soups can be very spicy because the Thai tradition is to use rice or possibly bananas to balance the chilli. Also most Thai sauces and curries will have considerable added sugar. A BG meter will really help to assess what spikes your husband while your traveling.
But my experience is that it is easier to keep BG under control with Thai food compared to Indian menus. If you are in main cities such as Bangkok, Chang Mai and Phuket there will be lots of Japanese, Korean, Italian and other international restaurants around. As worldwide, the more you avoid processed foods the less exposure to trans fats and HFCS. For breakfast focus on eggs, bacon if available and salad. Personally I am not keen on processed meat sausages, chicken ham, etc.
But your biggest challenge may be resisting the tropical fruits and fruit drinks, smoothies, etc on offer. Only diet drink available is Coke Zero/Coke Lite (latter is less sweet but can be hard to find). Fresh coconut juice may be OK, everything else will be very high sugar. Re alcohol, cocktails will always be high sugar, beer as everywhere = liquid bread, safest low carb drink option is whiskey and soda.
Hope this helps! Thailand is a great country to visit.