Vne has to be
IAS because it is marked on the Airspeed Indicator (ASI)
In flight, if you want to check you are below Vne, you look on the ASI.
You
don't look on the ASI, get your IAS, convert it (using altitude and temperature) into TAS and then check if the resulting value is below the ASI Vne marking. That would be completely useless.
What exactly does that article say?