I'm going to focus mostly on how useful this service would be, but first I wanted to make a comment about the ethics. One thing that Disney is absolutely terrific about is helping people with disabilities have an incredible day at their parks. They do everything they can to accommodate any and all disabilities. It's makes many a vacation more magical, and is something Disney should be commended for.
Unfortunately, there are always some people who try to game the system, even going so far as to "fake" a disability to try to skip lines. It's really unfortunate that this occurs. This tour-guide service is another system-gamer, essentially taking something very wonderful that Disney does for people who truly need the assistance, and "stealing" it for people who do not. It's appalling and hugely unethical. And, frankly, it's abusers like this that make it more difficult for Disney to provide assistance for those who truly need it.
How well this service would work
Putting aside the ethical issues, how well would this service work? If you're truly clueless, this service might hold some appeal. However, it's not as much help as you would think.
First, it's important to note that only a handful of older attractions have separate entrances for people in wheelchairs - generally the older attractions such as It's a Small World or Peter Pan. Those are the attractions where having a disabled person as your escort would help you skip lines. However, newer attractions (including most of Epcot, Animal Kingdom, and Hollywood Studios, plus several in the Magic Kingdom) generally have queues designed to be accessible to people in wheelchairs and motorized vehicles. For those attractions, having a disabled tour guide offers no real advantage. So you're basically just paying for their tour guide services for those attractions, and no magical "line skipping."
There are better alternatives at EVERY price level for skipping the lines!
If price is truly no object. Go ahead and hire an official Disney tour guide. They charge between $315-$380/hour, so we're talking thousands per day. However, you essentially get unlimited Fastpasses and will have your waits reduced dramatically. Plus, you get a Disney tour guide in a spiffy Disney uniform!
If price is mostly no object. Use an outside Disney touring company. There are a handful out there that are reputable and have very knowledgeable tour guides. You generally won't wait in any long lines and will see everything you want. Cost is generally around $1000-$1500/day. I'm happy to provide you with some reputable companies if you drop me a line.
If you want to skip the lines but at 1/10th (or less) the cost: Hire Optimal Magic! (You knew I'd put in a plug for me somewhere!) I provide personalized plans that are incredibly easy to follow and fully customized to your group and the days of your visit. Just like the services above, you will never wait in long lines, and your plans will be personalized and customized to your needs and desires. My services for an entire Disney trip cost less than two hours of a Disney tour guide and less than 1/2 a day of an outside touring company (including the unethical scammer ones).
The only difference between me and the on-site tour guides - I won't be there with you. (Some people consider this a good thing.) But no worries - everything will be planned out to skip out on all the lines.
If you want to spend almost nothing - Plan for yourself! If you're willing to put in a significant amount of time (we're talking 30-40 hours for a trip) and are good at identifying the good vs. bad advice, you can plan a trip on your own. But it can't be stressed enough - you really need to hunker down and do your research. A few "tips" from friends or reviewing a few websites for a couple of hours won't cut it - you'll end up in many, many 1-2 hour lines. However, if you want to plan it yourself, go ahead and give it a go! Email me and I'm happy to direct you to the best resources to plan for yourself.