I only ever worked for one JW, and I would have to say that he was an excellent employer. Mind you, he was an exceptional person (Having never known him before he became a JW, I cannot comment on how much his religion contributed / did not contribute towards that).
Otherwise, all persons I know who worked for JWs have been unanimous that it was a negative experience. This includes a non-JW friend of my wife's, who worked many years for a pest control company where senior management is still dominated by prominent Witnesses. (Down in this part of the world, many elders are not window-washers. Pest control is another occupation in which the JWs are overly represented).
Bill