There is no formal night on the 4-day. If DH is a guy who's comfortable on the upper end of the fashion scale, I would say pack a suit or sport coat. You can leave the ties at home. I know Disney has relaxed some of the dress code recently. I'm not entirely happy with that, but in the end, it's none of my business. The majority of people will still abide by the old school dress code, I think. That's generally a sport coat over a polo or button down at Triton's and a button down and jacket at Palo.
For me personally, I'm still going to get pretty to go out, especially to Triton's and Palo. And I wear business casual every day anyway, so khaki and a polo is nothing for me at Animator's Palate and Parrot Cay. But my theory is that if I'm going to a restaurant (landlocked or floating) where the description of the food is longer than six words (and none of those words are "breaded" or "deep-fried"), then I'm'a get all gussied up.