The values are meant for numeric RGB readouts of the cursor point only, by design.
I guessed that, but what is it good for? If I can't fix it to see a before after, I can see little any use for it. Maybe checking for clipping?
DNG PE is primarily intended for visual-based profile editing (i.e., look at an image while making adjustments to the control points).
So there is little difference to the old style color editors like in C1, except that there I can yes have real cursor point read outs.