Any screwball condition will alter the absolute accuracy of the static system, especially if the static ports see any head-on air impacts, but the high rate of descent of VRS is quite enough to be sure that you see a big indicated descent rate while in VRS.
BTW, lets uncan the great debate: VRS occurs at quite a bit more than 300 fpm, it must be about 3/4 of the rotor downwash velocity where the downwash cannot get out of the way of the descending rotor. This is always a much higher rate of descnet than 300 fpm.
Why do instructors say otherwise, and demonstrate "VRS" in slight descents that seem to "prove" otherwise? Because there is an increase in power required at 300 fpm, which can fuel a vast over-pitching that turns into VRS if left unattended. The typical VRS demonstration is actually a demo of increased ROD due to the unstable nature of a hover descent - where some ROD makes the power needed to hover rise a slight amount. When the instructor forbids any collective rise, the descent increases (not yet VRS, just a hairy increasing vertical descent) until real VRS can be experienced (at 3/4 of the downwash speed). The aerodynamics of VRS assure that it CANNOT be experienced unless the aircraft is at or near zero forward velocity and at or near the downwash velocity - somewhere above 750 ppm for a light helo, and near 1500 fpm for a big one.