Yeah, 'course it does. That's why it can seriously backfire on someone like Huskar, since he deals damage to himself and then gets the damage he deals back on him. Life Break is magic damage.
In any case, that's absolutely glorious... I laughed heartily. Of course, slightly specialized teamwork right there, but hey... Good for a show.
Just did a test on something, and found that Slark's stolen agility from Essence Shift does, indeed, factor into the blast done by Ethereal Blade. Also, Leap and Dark Pact both do magical damage and are thus enhanced on an ethereal target. Not something you're exactly gonna see on him a whole lot, but hey. Worth noting.
Which leads me to another thing worth noting, that I was inspired to test out by that video... Namely, that Nyx is even more broken than previously expected.
Blade Mail does not reflect reflected damage... Which is to say, if Nyx attacks someone with Blade Mail, his shell doesn't proc on the damage he gets reflected back at him. No returned damage, no stun.
HOWEVER... Other retaliatory skills, such as the passives of Axe, Razor and Centaur, DO proc the shell. Meaning they deal the damage to themselves, and also stun themselves... Even though Nyx was the one who started it.
So, put up a shell and mana burn Razor... Razor gets burned, damaged, gets his shock return damage back at him, and then stunned for the duration of shell's stun. Centaur is even easier, just pop shell and poke him once.
Note that Nyx's shell neither blocks nor returns the damage done by Axe's culling. Blade Mail, interestingly enough, DOES return the damage... But only actual damage done, namely whatever you had left of life before culling blade procced.