If the step wedge densities were truly neutral it wouldn't make any difference. When you measure density, you measure the light incident on the wedge and the light transmitted by it and get the log of the ratio. When you use that same wedge to expose film or paper, the color of the exposing light will make a difference. The exposed and developed film may or may not be neutral gray. It certainly will not be neutral if it was developed in a staining developer. This copy of the step wedge will look different to paper than a neutral density copy would. If the purpose of reading the neg with a densitometer is to predict how a print of it will look, the densitometer should have the same spectral response as the paper. The spectral response of VC paper varies with the spectrum to which it is exposed.
If that is the purpose, test strips are better that a densitometer for determining the printable density range of a pyro neg on any kind of paper.