It should work in theory at least, but you still have to recheck your bags

http://www.jetairways.com/MSIB21/Tem...ACHEHINT=Guest

Through check-in from Jet Airways to Northwest at Mumbai:
Passengers traveling on Jet Airways and connecting on to Northwest at Mumbai will have to hand over their bags on arrival to the NW security personnel present at the Domestic Arrival hall. The North Weststaff will then transfer the bags to the International Terminal. Please note this facility can be availed by passengers arriving into Mumbai between 1500 hours and 2230 hours. Passengers arriving into Mumbai before 1500 hrs and after 2230 hrs will have to personally carry their baggage to the international terminal.