While I'm not a fan of providers with drivers; I understand there are valid reasons a provider may utilize a driver ... either on an occasional or full-time basis.
Last year I dated two providers who utilized a driver. One was because she had a medical condition that prevented her from obtaining a driver's license. The other was because we were meeting in a major metropolitan area and she didn't know the area well enough to trust her own ability to get where she needed by the time she needed to get there.
I didn't know about the drivers in both cases until our date was over.
Professional escorts will only hire experienced, professional drivers due to the potential issues and the affect on their reputation if things turn ugly caused by the actions or behavior of a troublesome driver. Unless there is an emergency or some sort of trouble, a client shouldn't even know there is a driver unless the provider tells him.