Ahh, right.
Well, as vB is by default, I believe that this hack would achieve what you want. (ie: as far as the $postcount variable is concerned, it increases regardless of whether it was a reply or a post.)
Therefore, new replies OR new threads in the specified OT forum would not add to Post count, but would add to OT Post count. That's why I called it 'OT Posts Hack' and not 'OT new replies Hack'.