Spike isn't technically a 'stun' so I'm not really sure (Unbreakable Will does not remove the effect).

I suppose there's one way to find out!

Assuming torhead is correct it looks like a knockdown

Source:

http://www.torhead.com/ability/5HDJ5qS
I'm only level 31 so I have a ways to go before I get there!

If the damage increase on Nerve Wracking doesn't effect bosses I'm looking at one of these two builds assuming the theory crafters come up with something definative on Shroud of Darkness vs Swelling Shadows:

W/O Swelling Shadows:

http://www.torhead.com/skill-calc#200rIMckrsk0sZZf0cM.1
With Swelling Shadows:

http://www.torhead.com/skill-calc#200rsrckrsk0sZZf0cM.1
If it does I'd definately make some adjustments to use it.