On my SR20DET, I was going to T off the factory oil pressure sensor for the greddy sending unit for my gauge. I did some research though and it looks like the stock 1-wire oil pressure sensor is just basically an on/off switch for the dash dummy light. If it sees <3 psi (the number I found), it grounds out and the dummy light on the dash turns on. Since I'm going have an actual gauge (mine are peak/hold/warning gauges too) I figured the factory dummy light is useless anyway and I just replaced the OE sensor with the Greddy one.

Even on a VTEC car, the VTEC solenoid on the head has it's own dedicated oil pressure sensor, so the stock sensor on the back of the block is probably the same style/dummy light sensor.