It's funny to read all the people here who are forced to dress up for work everyday, so dressing down is what makes it feel like a vacation. I can relate in a completely opposite way.
I work from home half the time, and on a film set the other half. I make costumes and spend most of my working time wearing the worst stuff I own because it's going to get dye, glue, threads, bits of fur and feathers and other nonsense all over it. When I'm not doing that, I'm homeschooling my kids and am likely to be covered in paint, more glue, and food. My husband is a stuntman and spends most of his time in workout clothes. We aren't religious so we don't even get to dress up for church.
I am literally DREAMING of wearing nice clothes on our vacation. I am so darn excited at the thought of a formal night where I can get a picture of my whole family wearing really nice clothes. I'm daydream shopping for the perfect dress to wear to Remy. I. Cannot. Wait. To dress up!
That said OP, I cannot imagine anything your DH would have any interest in wearing to dinner that would ruin my enjoyment of anything my DH or I are wearing to the same dinner. Seriously, I will be so busy ogling my DH in his suit on formal night, adoring how cute my children look in their fancy clothes (that they will probably wear exactly ONCE but it will be worth it!), and feeling insanely pretty myself to even notice what anyone else in the room is wearing.
Honestly, I've never understood why anyone would care what someone else wears to a restaurant. Going out to eat and going on vacation are supposed to be about relaxing and enjoying yourself and taking a break from your daily grind, not judging everyone around you.
As long as you're not wearing disgusting, smelly, or grossly revealing clothes to dinner, who cares. It's your vacation. If the thing that makes your hardworking DH feel relaxed is wearing shorts to dinner, let him wear shorts to dinner. If it's allowed by Disney, there's no reason anyone should judge. And since there will always be people who judge no matter what you do, you might as well relax and not worry about them. As long as your decent and abiding by the rules, you're not hurting anyone.
And now I'll step down off my soapbox, stop using this lovely forum as a procrastination device, wipe the paint off my neck, pull the feathers out of my hair, and get back to sewing.