In its original configuration, the 350 had no M/R droop restraint system. It was made available as a field retrofit in a Service Bulletin some time after the aircraft entered service.
For what it's worth, the Flight Manual states - "Of a semi-rigid design, the STARFLEX ROTOR HUB has no bearings nor lubrication system."
Note that it is the STARFLEX that is referred to as semi-rigid, not the rotor system.