The pressure of interest is the pressure supplied to the bearings. For most practical purposes, this is the pump outlet pressure. This applies if the oil sumps (bearing boxes, in other words) are at ambient, atmospheric pressure.
But some turbine engines have an internal sump at higher pressure, because of the vent system design. In this case, the pressure difference between the pump discharge and the sump pressure is of interest, because that is the effective nozzle pressure.
When this is the case, the displayed pressure will probably be a "delta P", in other words measured by a differential pressure instrument; Oil pressure to the "high side" and scavenge pressure to "low side".