The three tags you mentioned are already included in makeDNG. As for their values, the white balance (‘as shot neutral’ I believe) will be very close to 1,1,1 (I control R, G, and B exposures), the black subtraction levels from camera are per CFA channel but identical in value so one value is probably enough, and the ColorMatrix2 (produced by Adobe Dng Converter) is identical to the one you listed. Now, the matrix values are most likely wrong because the color separations effectively takes the camera color space out of the equation. I think I need to look into the ICC profile linked by rom9 in ‘Any interest in a “film negative” feature in RT?’ (post #177) and see if I can extract something from there.
There are of course other mysteries in Adobe Dng Converter processed .nef. The white level listed is 15892 while dcraw tiff has all saturated pixels at 16383.
In addition, the pixel values appear to have been scaled (in camera or during decompression) because the histogram has more or less evenly spaced gaps (every 6th or 7th value has zero samples for red and blue, and every 40th value for green); irrelevant but annoying.
Come to think of it, this was the rabbit hole I tried to avoid…