I was following your argument and nodding in agreement but you lost me when started trying to correlate the location of the cracks with the location of the rebar.
Concrete will crack, that is a given, the trick is to control the cracking. My assessment just by looking at last couple pictures, is it appears that it is a mass weight problem causing strain (tension) on the slab placed on the slope. Concrete does not resist tension very well, which is why we use rebar, and cracking will occur throughout the slab, not because of the rebar location. I would take a look at the slab pouring plan. In other words are they skip pouring individual slabs, by skipping every other one and then coming back and pouring a slab in the gaps after the other slabs have cured, or is this just one long continuous pour? What is the size of the slab? Slab panel joints are usually quite small and not greater than 15ft x 15ft. Anyway just some thoughts.
Based on the pictures I have seen the cracks do not appear to be randomly distributed. One testable hypothesis is that location and distribution is related to elastic deformation of the underlying rock. This may or may not be a contributing factor (as you pointed out, concrete will crack, especially under tension).
Given the history of this dam and what is now publicly known about the rock under the spillway, I certainly hope the non-random pattern of cracks have been competently investigated and have been shown to be benign.
Given what we now know about the way the DWR has performed in the past, I have my doubts.