As an update to my still ongoing dialogue with the "friendly" DxO rep, after more than two months she regularly informs me that they're still "working on it." At her request I've sent them several DNG photos directly from my SD card from my Ricoh GXR M-Mount for them to examine. Needless to say, at this stage I'm no longer hopeful that they'll be able to resolve "their" DNG problem.
After several more email exchanges over the past few weeks with my still-friendly DxO rep, she has finally informed me that:
"We currently support the Leica:
M (Typ 240)
M9/ M9-P/ M-E
and that does include .DNG support because that is the main image format.
However, the GXR using the A12 Mount will not show up as supported, so unfortunately they will not be able to be corrected. I am not sure why we did not support the GXR and you are correct that since it is being discontinued I doubt the module will be created.
Please let me know if you have any questions."
So, I guess the case (for me anyway) is closed. But she does, as you note, claim they do support DNG files from the various digital Leica models themselves."