If the driver isn't willing to comply with the regulations, then they shouldn't broadcast their services on Uber.
An individual driver is not required to. If that particular driver can't, Uber still has to provide that service for the passenger.
Instead, the ADA says that companies must make reasonable accomodations for the employee.
In this case, it means drivers with allergies don't have to take animals in their cars.
For someone with a back injury, it might mean they can stock shelves so long as items are kept under a certain weight.
There are plenty of instances of people with disabilities not having to do the full job, because they can do most of the job.