Is it a violation of the Muslim faith for a taxi driver to accept a person with a service animal as a passenger?

No. A Muslim person is required to carefully wash and change clothes before praying after contacting a dog's saliva, but a taxi driver should not be exposed to such contact from a service animal, which is highly trained and well-behaved. It is a violation of the Americans with Disabilities Act for a taxi driver to refuse to carry a passenger because they have a service animal.