I do drive a company Van that is fitted with a gps tracking device. It has helped me when I had a competitor (acting as a civilian) call in my van number and tell my service manager that I was doing 80mph and swerving all over the road. The gps showed me doing exactly the speed limit, exactly where I was supposed to be. Without it, I would possibly have gotten a write up. Now on the other hand, I've had to move my van on a saturday to snowblow my driveway (I live in Michigan), and got a call first thing monday morning asking why I had my van running after hours. Once I explained myself I was in the clear.
To me it's necessary since you can never trust anyone in this world, but the problems occur when the management confronts an employee in the wrong manner, as if they're TRYING to catch you doing something.

-The eye in the sky doesnt lie-