I have not heard anything preventing you from having paint protection such as a ceramic coating on a Motability car.
With Matte you must use a liquid sealer designed for Matte paint. Like any good valeter will tell you a liquid sealer such as ceramic sealer will only last 2-7 years and also very much depends on the quality of the product to its lifespan.
The quality of workmanship between a valeter and dealer valeter is leagues apart. A valeter will take the time to apply any coating, get into all the nooks and crannies, ensuring the job is done to an high standard vs slap dash quick job by the dealer.
As well as washing ever week or two, you will still need to decontaminate the paint at least every year if not every 6 months using a matte paint cleanser.
The slightest scratch can’t be buffed out, as it can with other paint finishes.