"However, when it does stall, the Dauphin pitches forward and left very violently. Doubt if that was what happened on the video."
That's exactly what it is doing, is it not? From the initial pull up, the aircraft bunts and rolls left, ending up level again and rocking laterally from the subsequent PIOs.
What surprises me is that such a benign pull could induce jack stall on a twin hydraulic system aircraft. The 155, which although with a different head design, shares many common hydraulic system componants, can be thrown around with real abandon and no ill effects. There is a servo accumulator for the RHS system, but it is only there incase the system fails and it then assists the LHS system while the pilot regains level flight. Even then, it is only there for extreme manouevering.
I have to say, GIC, I'm a bit disturbed to hear that someone has shown you this effect during a conversion. The loads that must be imposed on the airframe in carrying out this demonstration would be large. I can't see it happening with much less than 3.5 - 4 g and that hardly qualifies as FLM territory!