How will Ambush (100% more crit chance vs full life) interact with crit snapshotting?

"Is crit always rolled per hit?"
As mentioned in the quoted post, Crit is always rolled on a per-activation basis. It's the very first sentence dude :P

'All Crits or all non-Crits' has never been true due to Critical Weakness (now Assassin's Mark), and the Crit confirm roll further pushed it into not-true territory. It's just an easy way of saying that Crit is rolled per activation, as opposed to per Hit.

It's "true enough" in practice: you won't really notice that you sometimes fail a Crit Confirm all that much. The fact you didn't know it wasn't true is testament to that! :)