For skins in the upper half of the fuselage in bending tension, the pressure acting on the skin is just adding to the tension stress on the skin from fuselage bending, so it doesn't help there. For skins and stringers in areas of the fuselage where loads are in compression, the pressure if anything will displace the structure (bulge it out) in effect "bending the column" and making it less able to take compression loads (maybe only a few thousandths of an inch, but still something). On the other hand, the pressure will tend to help keep the tube circular, so it will probably tend to reduce stress on circular frames that are resisting the tube from collapsing in bending.
The most stressed area in the fuselage is compression stress at the bottom just behind the wing, (next to the pivot of the seesaw you might say) and there is usually a heavy compression beam structure down that that is not helped or hindered much by how much pressure is acting on the pressure hull.
Overall, none of this is taken into account in the structural design and there normally aren't any specific structural restrictions between pressurized and unpressurized flight as far as G loads go. For example, you won't see different published G limits, or Turbulent Air Penetration Speeds, or Maneuvering Speeds, for pressurized and unpressurized conditions.