Usually, yes.
You raised some examples, and there are many, many examples of the kinds of monitoring that can go on, some of which is related to the work process in which employees have rights. I'm not sure this exactly answers your question, but one of the arguments for employers to monitor is that they're responsible for the work of their employees. If I sit at my computer and send out a message harassing some individual, my employer is responsible, because I'm using my employer's equipment on my employer's time. The employer could legitimately say they have a perfect right to monitor, because if they're going to have legal responsibility, they have to show they took steps to be in charge, if you like, and to be aware. And this covers a whole bunch of activities, not just harassment: it could be trade secrets; it could be going to sexually explicit websites and creating problems in the workplace, and lots of things. So those are part of the work process. Clearly the employer has a right to monitor.
The questions that arise are what about how fast the employer is entering data into the computer; what about how long the employee is spending away from the desk, away from the computer; or what about monitoring in rest rooms? Recall the infamous case of Canada Post, which had video cameras installed in the men's and women's bathrooms because of concern about drug usage while people went to the bathroom. There are devices installed to make sure that restaurant workers are washing their hands before they leave. We all say, oh great, we hope they wash their hands, otherwise, who knows?
So there's a whole range of these things, and many have quite legitimate purposes. It would be hard to argue it is an intrusion on the work process.