Richard, you can do Kelvin tuning on the GH5 natively. Put on the RGB overlay on the DNC and you get the same tool - maybe not as effective as with the Atomos, but it works (see Kelvin in upper right corner with up and down arrow to adjust)
Is the overlay at the bottom of the screen generated by the DNC monitor, or by the GH5 itself? Does the DNC have any options for displaying false color or zebras (for exposure)? How about peaking/punch-in and/or other focus aids?