I have only flown a heli a few times under instruction (R44) but am curious if it is even possible for a very competent IR rated heli pilot to safely fly a non certified (for IMC) helicopter in these conditions?
What do you mean by "these conditions"? If you mean at 200 AGL in fog, I don't think anyone can do this "safely". I don't really see why a competent instrument pilot couldn't fly an R44 in IMC under proper IFR conditions, i.e. at a sensible altitude and prepared to fly an appropriate approach at the end of it. Of course it's not legal, and in a heli the excuses for inadvertent VFR into IMC are pretty thin since you can always stop before you enter the cloud.
fwiw... I have about 1900 hours mostly fw, a current IR, and about 150 hours heli time. I was working on my CPL-H (I have a CPL-ASEL) and did the requisite 5 hours under the hood in an R44, mostly at night. I wouldn't be scared at the idea of flying an R44 in IMC, though it's just about impossible to imagine how it could happen.
I hate flying under the hood - it's like some kind of sensory deprivation torture. I much prefer being inside the real thing, where I can look around and see everything inside the aircraft. IMC is scary if you think it is, but quite relaxing if you don't - though it does require 100% concentration to hand fly.
I believe it's the case that you need an autopilot for heli IFR. For sure it's impossible to mess with charts, iPads etc the same way you can fixed wing.
None of which changes the incredible stupidity of the pilot in this case, and the tragedy of killing three innocent people for no reason at all.