10 minutes later...
Ok, it does always pay to listen to people's advice. I went back and read the PDF for materials making. It says:
"Dye Transfer works by creating a relief image in gelatin. The thickness of the gelatin on the matrix is proportional to the amount of exposure the area receives. This is accomplished by exposing the matrix through the base. A yellow dye is incorporated in the emulsion, which absorbs the blue light to which the film is sensitive. The exposure proceeds to a greater depth into the emulsion with greater exposure. The film is developed in a pyro tanning developer that cross-links the polymers of the gelatin in exposed areas, and ‘hardens’ it, or makes it insoluble in water. The film is then washed in very hot water, and the unexposed gelatin washes off. The matrices are then soaked in dye baths, and the dyes migrate into the gelatin relief image on the matrix. The matrix is rinsed, and then rolled into contact with the receiver sheet. The dye transfers from the matrix to the receiver."
And indeed, there is no mention of K-dichromate in the emulsion making. My simplication was way too simple.
Instead, it's hardened in a tanning (pyro) developer. So my question is, is gelatin hardened in a tanning developer fundamentally different than gelatin hardened by K-dichromate?
And obviously the matrix must be washed and the soluble gelatin removed.