My Kenwood DMX1307S comes with a GPS unit, can't you buy one of eBay for yours? Did you check to see if there's a conversion cable for your van? I know there's a few types of conversion cables available, but I just use the one that comes with the unit.
It "ought to work". I'm almost certain all gps radio wires are expected to work the same way and I don't see Joying or Nissan as attempting to re develop it.