Unfortunately for Setterfield, there is more to it than just what you call "the Doppler hypothesis." There are several independent lines of evidence which all give the same result. The Four Pillars of the Standard Cosmology.
Additionally, there is yet another line of evidence: the Lyman Alpha Forest.
Setterfield needs to undo all of cosmology, and construct something else in its place that is consistent with all the relevant evidence if he wants Genesis to be scientifically accurate. Merely dismissing the Doppler "hypothesis" (it's more than an hypothesis regarding the redshift these days) isn't going to do it for him.
Hands will be waved. "All those things would look the same under cDK."