I tore my meniscus a few years ago and I had a good experience with the surgery. I recovered in a decent amount of time without any therapy. I struggled a bit as the doctor found an additional problem (I dislocated my kneecap pretty bad...) and that part still bugged me after, but I had to wait for 2 more months before I could have that fixed... Since then I still have great movement in my knee. Granted, I can't get it to bend as good as before, but I can still sit "Indian-style" (is that still the term??? is that even PC???) and can cross my legs with no problem or pain.
I have been to Disney (land and world) on the DL and if you plan ahead, you'll have a great trip with limited interruption (plan to take some sit-down breaks: pop in a sit-down attraction, use a park bench to enjoy the view, eat).
I have gone on both crutches and wheelchair. I would recommend being prepared to have him in a chair! It is a lot to walk, and there is no sense in being miserable and further causing inflammation in a surgically repaired OR pre-surgical knee. It's not worth the discomfort and the risk of additional injury.
Keep anti-inflammatories on hand. (Ibuprofen, aleve, naproxin) If he doesn't have a script for an anti-inflammatory I would ask for one, otherwise I recommend taking advil or motrin several times a day (but obviously not exceeding the daily allowance) at least 4-5 days ahead of time to help quell the inflammation in the knee before you go - get a leg up. (Just remember that you can't take them for an extended amount of time - found it's bad for the heart)
Have some pain meds (again, I'd ask for a script). Nothing too strong though so he can have pain management, but not be so out of it that he can't enjoy the trip.
I have arthritis in my back and did the anti-inflammatory push 4 days before our week-long trip. I also had some ultracet (script from dr.) on hand for major flare ups. I didn't have to use the pain meds every day, I think I took 8-10 pills the entire time I was gone, but I knew that I had a back up plan in case it got really bad.
I've had over 16 surgeries in my short life (mostly foot and ankle, 2 knee, 1 on my thigh, and 2 c-sections [planned for baby probs]) and have had to dial in a system so I could continue to enjoy the things my parents took us to do. It is perfectly reasonable to travel with injuries as long as you plan smart and are prepared. Talk to your doctor about a regime that is best for DH and the best of luck! I hope you guys have a magical trip!