Actually TR, the 365N and N2 do, as you say, have a secondary hydraulic system for the undercarriage, but the pump for this is powered by the same shaft as the left hand hydraulic system. They have an electrically powered emergency pump only for lowering the undercarriage in the event of a failure of the secondary system. The only actual hydraulic accumulators are in those aircraft with an assisted braking system, which enables the brakes to be assisted a few times without activating the hydraulic pumps, so that e.g, if the aircraft is parked with the rotors stopped the brakes can still be re-pressurised after moving it.
The so-called 'accumulators' to prevent jack stall are actually incorrectly named. On the top of one of the lateral servos, powered by the right hand hydraulic system, there is a small chamber pressurised to a preset value through a calibrated orifice and holding open a microswitch against a spring. When the aerodynamic loading on that jack approaches a point just short of actual blade stall, the force is sufficient to overcome the hydraulic pressure, close the microswitch and bring on a 'Limit' caution light to warn the pilot of impending jack stall so he can decrease the severity of his manoeuvre and offload the jack.
Hope that helps.