All of us have experienced answering services that warn us "This call may be recorded for training purposes". Companies routinely record phone calls to monitor and train staff in the handling of customer service requests and complaints. At Arrow, we're a small office, so I don't record calls, but I can listen in on a conversation, and give staff feedback as needed. Still, recordings are useful because they are objective. You can't argue with a recording - you can hear both the words and tone used.
Video takes it to the next level because it shows body language and circumstance. Video is clear and makes it impossible to argue the facts of the situation. There is no "He said, she said".
As an employer, have you ever considered using a webcam to record your interactions? If you have a webcam, you may have footage of how you manage or train your employee. Why not review the footage? Take an objective look at your communication style: pay attention to your body language and tone of voice. How good of a communicator and trainer are you? Would you feel comfortable allowing others to view footage of you interacting with your helper? What kind of communication with your spouse and children would it show?