What kind of things does the iPad display? Should the safety driver even be tasked with looking at it while in 'control' of the vehicle?

If you search "Uber autonomous vehicle" you can see some videos of the display. From what I gather, basically gathers the signals into a human readable model. In general I wouldn't have recommended this driving style but it might have been too dark to see much anyway.

I don’t understand this, I’ve seen a few people comment in the same vein.

People can safely drive in total darkness with the aid of their amazing human eyes and high-beams.

If for some other reason visibility is low you slow down - not rely on glancing at a backlit display ruining your own night vision and taking your eyes off the road for seconds at a time.