Helicopter mast bumping in low g condition The helicopter shown in the concrete pouring video seems to taking off from a hill and descending down in a way which can be classified as low G with low rotor loading. Although, the helicopter is three-bladed, mast bumping should be less of an issue, but from my understanding still worth considering.
Could a maneuver like this be executed in a similar way with a two-bladed helicopter such as a Bell 206 or Robinson. Furthermore, what is the reason for mast bumping being less of an issue for helicopters with more than two blades?

                
            
The famous video of the US Army seems to be describing exactly the condition as shown in the first video as potentially dangerous.
The answer is yes it could be used in that flight profile as the pilot of that AS300 was never in a low G condition with the rotor unloaded during those maneuvers.  Once he dropped the concrete, though he’s descending, he’s also accelerating at a high power setting, which is keeping the rotor loaded.  However, zero G mast bumping is still a risk that must be considered and thoroughly mitigated for during preflight for all helos with a semi rigid rotor system.
Mass bumping only occurs on helicopters with a semi rigid or teetering rotor system. It has to do with how a semi rigid rotor is supported by the mast in an under slung condition, where excess flapping can result in mast bumping.  It will generally occur in conditions like zero-G pushovers at low power settings or when attempting a steep slope landing.  Mast bumping is not possible on rigid, fully articulated, or elastomeric rotor systems where the rotor mounts cannot strike the mast, even with excess flapping.
Here is a pretty good recap on the subject of mast bumping.

                
            
Even helos with two bladed semi-rigid rotor systems can be flown through some pretty extreme maneuvers, provided the pilot flies within the design limits and does not unload the rotor.  I remember West Coast JetCopters, who provided the Bell 222 for the television series Airwolf, did some pretty extreme flying on those choppers and a 222 does use a teetering rotor system.  They just had really, really good pilots at the controls.  See 0:57 in the video below where the stunt pilots put a 222 through the helo equivalent of a hammerhead stall.