The accumulators only provide the same or less pressure than the normal hydraulic system, so they won't provide anything extra in the jack stall situation, which is when, as I understand it, flight loads exceed the capacity of the hydraulic jacks to oppose them.
If the aircraft had great big kick-arse hydraulic jacks and enough pressure to move them, jack stall wouldn't be a problem.
As it is, I've only felt it when trying to induce it on purpose for demonstrations - high speed, high power, pull reasonable g, feel feedback, reduce severity of manoeuvre and reduce collective, feedback goes away.
Depending on the condition of the particular hydraulic system and how the aircraft is being flown, plus gust loads perhaps, it seems it can happen in less severe flight regimes - close to the ground, not good as in this case.
The continuing flight after the tree strike thing doesn't sound that great, though.