Not necessarily. Jazz basses with the metal 'Bell Plate' provide a mahoosive ground connection to the pots, because both the output jack and the pots are in contact with it the whole time. This is fine until a pot comes loose on a gig, and you start to get intermittent drop-out.
P basses tend to have plastic plates with a thin layer of conductive foil on the back, so in theory should be grounded via this.
Soldering wires between the 0V (ring of the output jack) and the pots shouldn't strictly be necessary, but it's a 'belt and braces' approach that I prefer.