If 99% of drivers check that box, and it affects service times, then they will have to come up with some other option to accommodate the drivers. Prove the allergies or something, since some of them are certainly lying with prevalence being 10-20% in the US. And it would have to be a best effort, the rider with a true service animal is legally protected and a driver with allergies or fear is not a legal reason to reject service altogether.
I don't think you are allowed to require riders to say they have a service animal when requesting a ride.
I would think Uber would want to handle those sort of compliance issues before the driver gets there. As you don't want the driver to get something wrong. And it just makes things smoother for everyone.
Not sure if they can require a rider provide this information ahead of time, before pairing a rider with a driver. But if its voluntary, I don't see any problem with making the process smoother for everyone. Again IANAL, so could be off base though.
And now that the system knows someone has a service animal you can automatically review any cancelations by the driver and look for problems. I am actually kind of surprised that there isn't some review system already in place when a driver ends a trip early on someone. Unless the rider changes the destination, how can the driver not drop them off at the agreed upon location without getting flagged somehow?
Could even in rare cases, if there are absolutely no drivers without allergies around, offer them a bonus to take the rider anyways.