I agree with everyone else, yelling should never be okay.
And raising tone of voice should be used cautiously.
I had a t once who raised his voice at me during a time that I needed gentleness. It really messed me up and made me feel worse.

And no t should ever make their client feel bad, in my opinion. They should help the client to realize what they have done or been doing was wrong but they should not try to make their client feel worse!