No measurable performance gains, no codes, only POSSIBLE issue is that the DV valves are designed to work on DP. this means that the little diaphragm that is inside the DV will open based on MAP tube PSI-Charge pipe PSI=Diaphragm opening pressure. If there is no MAP tube pressure this means that the valve may open prematurely or open later than desired.
However, if the diaphragm is only designed based on force pressure (pressure in the charge pipe) then there is no worry at all because the only time the diaphragm flap will open is based on pressure shock...(when pressure is built (turbo spool) there is a small tube or channel that circulates around the diaphragm that presses the diagram closed under boost, and when you rapidly let off of the gas pedal (decrease in force pressure) the remaining pressure in that little channel will act as a low pressure venturi and suck the diaphgram open.
this is similar to how an expansion tank works in a hot water circulation system in a commercial building.