Technically no you don't have to apply the factors to the QRH because the performance is intended to be used in flight, ie after dispatch. The despatch rules do not apply in flight.
The point of VNAV is to give an idle descent from T/D. Not sure why you would want to use VNAV path to descend at a specific ROD, the only way I can think of doing it is to create 2 waypoints with hard altitudes and a set distance apart.
For example, say ground speed of 300kts or 5nm a min, so for 2000fpm RoD, it would take 5 min to loose 10 000ft, in which time you cover 25 nm over the ground. So 2 waypoints seperated vertically by 10 000ft and laterally 25nm would do it. Much easier to use V/S or LVL CHG.