Unless otherwise stated, the voltage rating of wire may be assumed to be an AC RMS rating.
That is 600 volt wire, if otherwise suitable, may be used on a 600 volt nominal AC system.
A 600 volt RMS AC system will have a peak voltage of about 1.4 times the RMS rating, or say about 840 volts. No de-rating is required since the wire is designed for 600 volts RMS, and therefore by inference for up to 840 volts peak.
Therefore the use of such wire for the output of a VFD should be fine provided that the RMS voltage does not exceed 600 volts RMS/about 840 peak volts.
As regards high voltage pulses from the control gear for HID lamps, if the high voltage pulses are confined within a luminaire, then this is an appliance and outside the remit of the NEC. The luminaire should of course be UL listed or equivalent.
If however an electrician uses standard wire to connect a remote ignitor to a lamp, than IMHO that is a violation.
If a standard type of wire is supplied pre-wired by the manufacturer, then it could be argued that this is part of the appliance, and if the complete kit or assembly is sold for the purpose and UL listed, permitted.