Not quite sure of the terminology being used here. N2 is the term used to describe the rotational speed of the power turbine or free turbine as it is variously known. The power turbine is driven, as stated, by the exhaust gases from the gas generator (engine to you and me) and so has a fluid coupling but no mechanical coupling (hence the term, free turbine).
In the cockpit, N2 and Nr are normally on the same gauge, and in powered flight read the same value (normally a percentage figure). In true autorotational flight the needles will be split, ie N2 will be lower than Nr and the freewheeling mechanism will have disconnected the transmission from the engine (free turbine) input. In this instance, it wil make no difference whether the engine is running or stopped ie practice or for real. If, though, the needles are joined, then the engine will be contributing some power to the transmission and will be assisting the autorotative section of the blades with maintaining Nr, and hence the performance may be better than in the event of a real engine failure.
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Another day in paradise