i'm listening to what I think is the segment now ... very small sample of therapists surveyed though and it mentions 9 out of 13 therapists dreaming about their clients over a 1-3 year period; and of that about 6% of their dreams were about their clients

BBC World Service -Therapists? dreams

one reason given for not telling clients is they thought it might be creepy for the client

this article is also based on the research mentioned on the program

What happens when therapists dream about their clients?

the article also mentions they were student psychotherapists which might also impact the results