Lee,

as soon as you select a filter and expose your VC paper, you have in effect assigned that paper a gradation. Even if you use for example a 2 1/2 filter, by using the 2 bath development method, you can further influence the tonality of the paper.

As for split toning, I do not have much experience in this area, but I don't think that split toning can be used a reliable source for influencing the shadow detail or over all contrast in a print, atleast not in a way that could be repeatable on a consistant basis.