If it's on company property and the workers are given notice that it's happening then I guess you can say it meets an ethical standard...that doesn't make it a good idea though, a great deal of time and effort will be spent trying to circumvent such tactics and good luck having your employees trust you after, if your employees are doing what they are supposed to do and meeting their expected performance, there's no other reason to surveil them except you're a mini fascist control freak