What are you using the row count for?
Adding the expression =NoOfRows(Total) seems to work in the body of the chart, but not in the title. It isn't clean or elegant but if it is really important to add it will put the number of total rows on each line.
Not that it will help in this case (for the web browser view) - but I have used macros similar to the following and added triggers to update automatically when selections are made:
ActiveDocument.Variables("vRowCounter").SetContent object.GetNoOfRows, TRUE
This will only be used in the browser, so I am limited. I do want the count in the title - it's sort of a standard for other dashboards in the company. This one is different in that the dynamically hidden/unhidden dimensions mess up the way I have counted before. I was hoping that someone has crossed this bridge with hidden dimensions, perhaps in another context.