While the extra bolts from Runaan's Hurricane DO proc Ashe's Frost Arrow passive, they WILL NOT crit because she has no normal crit chance normally anymore. It might be intentional, I'm not sure but it just felt weird to me :)
Runaan's Hurricane does not apply critical strikes on anyone, as it scales off of your AD, and not the damage done by the actual auto attack
they will not crit, because they dont crit in general.
mechanically all of ashes auto attacks against frost shotted targets crit. you can see this because she gains the frenzy buff and gains up to 15% attack speed, even when she doesnt have crit items in her inventory.
this alone is rather huge. other ad carries only fully profit from the mastery by lategame, when they crit reliably enough to stack the buff fast enough, before it runs out.
ashe fully profits from it from level 1 on, and effectively gains 15% bonus attack speed against a target she attacked 3 times very early on in the game.
