Theoretically, on a closed wet sump oiling system, the static pressure within the crankcase will have no effect on the oil pressure to the bearings and valves. Your gauge pressure will read lower, because it will be comparing the actual pressure at the pump within the closed system (say 40 psi which is against an internal static pressure of -7 psi) with atmospheric pressure (which your gauge reads as 0) so the gauge might read 33 psi. The same will be true of a dry sump system, as long as it is a closed system. On my old BSA, the dry sump tank is vented to atmosphere, so I'm a little concerned about the sump pumps ability to pump against the internal vacuum. But I'm only hoping for about a vacuum of 7-10 inches of water pressure (about 1/4 to 1/3 of a psi) so I'm not too concerned.