This is standard on practically every golf course; they want to fill foursomes so singles will always be paired with another group (availability prohibiting). Your husband should not have ANYTHING to worry about; in fact, he should look forward to this opportunity.
How does he play back home? Does he have a regular group and never play with random singles?
A golf course will not care what ability level or handicap the single is and/or the group they are pairing him/her with. It's simply a factor of filling tee times and available space. The exception (which is rare) is when a golfer will make the golf course aware of their ability and ask them to let other golfers know. In that case, the course will ask the group ahead of time if they are comfortable playing with said single. Basically if you are that worried about playing with drastically better golfers and holding them back (?) just let the pro shop know and they should take care of it.
I've been playing golf as a single my entire life and had the most remarkable experiences when paired with strangers. Sure there are the rare cases when my companions are jerks/inconsiderate/un-friendly, but they are so few and far-between and so dramatically overshadowed by awesome/friendly/interesting people that I don't give it one second of thought. I mean, especially if you husband will be golfing at WDW! He might be paired with cast members, executives, tourists, etc; I'm sure he'll have fun.
As for the Disney courses themselves, they range in difficulty and, thus, price and quality of golfer. Do you know which course he's going to play? The Magnolia, Palm, and Lake Buena Vista are all 18-hole championship courses where you will find the widest range of abilities. Oak Trail, their 9 hole walking course, is more geared towards beginners and is pretty easy to walk on. It sounds like he has a tee time at one of the big 3.
This might be a totally unnecessary tangent but I had a really weird (and disappointing) experience the last time I played at Lake Buena Vista (this has NEVER been the case at Magnolia or Palm, btw). I like to review the scorecard before I tee-off and kind of plan out how I want to attack the course, including which tee boxes to play from. For some reason there wasn't a card in my golf cart so I walked up to the starter and asked for one. He refused to give me one! He said they only give them out AFTER you tee off so they can be time-stamped to track your pace of play. Everything was about pace of play. He couldn't say that enough. I have never experienced that before; a course NOT giving you a scorecard. Either way I never once saw a marshal or encountered an employee enforcing this mystical "pace of play" policy that was apparently so sacred. It was just a really weird and slightly unnerving experience.
Anyway, he should be fine! Enjoy the views and the mickey-shaped bunkers!