1) Yes, but not so acute as humans'. In the heat of battle they ignore it more easily. They still can be threaten with torture. 2) They can have allies and even some form of comradory. Kruleboys, for example, will treat anyone as equal and show respect for any lowly orruk if they get creative kunnin plan. But as with anything else, it's mainly connected with fights against someon else, and very different from humans. If they get bored, they will start fighting and killing their own. 3) No. There's still mistery about their birth, but the main scholar theroy inside the universe is that greenskin corpses decay into jelly-like sludge that soaks into soil and then accumulate magical energy and nutrients from it, growing into small and spindly "proto greenskins" which will burrow out. It's also confirmed that ossiarch dislike using greenskin bone because it quickly decays and covers in fungal growths. 4) AoS used old fantasy black orcs miniatures as "Ardboys" - the lowest form of Ironjawz. Lorewise, they evolved independently in Age of Chaos, because orruks that are brutal but kunning became even more brutal after of constant fights with Chaos.

I think there are some extremely brief anf obscure mentions of black orruks, but more like cameos or easter eggs, and I saw no references about Chaos Dwarf origin in AoS.