Datsun installed it in conjunction with the fpr for a reason. If the fuel pressure supplied to the regulator is pulsing, then the pressure yielded by the regulator will fluctuate as well. Picture how the regulator works. It's an adjustable restriction in the return line to the tank, referenced from intake manifold pressure. It won't adjust to fluctuations in the line leading up to it, and so the pressure in the fuel rail will be uneven. After the regulator these fluctuations might be evened out, but by that time the fuel is just returning to the tank. The fuel pressure on the injectors is what counts.
That said, with a quality pump and no restrictions leading up to the pump, fuel pressure fluctuations shouldn't be an issue to begin with. I no longer run the damper with my walbro pump and the pressure is perfectly steady. I never tried running the stock pump without it, though.