| The two sections of a humbucking pickup and the two pickups on a traditional jazz bass are made with the coils wound oppositely. This allows the hum from one pickup to be canceled by the hum from the other pickup. And, yes, you can do the same thing by flipping the phase of one of the pickups on a jazz bass that uses two identical pickups.
HOWEVER, pickups that are designed to cancel the hum have two different magnetic polarities in the two pickups or two sections. This produces string signals that are in phase and add constructively when you wire them together. If you invert the phase on two identical pickups BOTH the string signal AND the hum will cancel. Nobody likes that!
So, to make this concept work on a bass that uses two identical pickups you would have to invert the magnetic polarity on one of the pickups in addition to wiring them out of phase. You may be able to do this on some pickups, I wouldn't know for sure since I have never tried it. But it is not as easy as simply flipping the phase on one and that is why the situation causes such an uproar.
Ken | 
