Quote Originally Posted by Alistaire View Post
0 damage prevents knockback in Ifrit HM plenty of times.
With some abilities yes 0 damage prevents knockbacks. Some other abilities do not.

The last boss in Brayflox HM for example will push you despite taking 0 damage.
Demon Wall, Landslide, and so on that have a pushback will not if you take 0 damage.

Trial and error.