League-of-legends – Does Warwick’s ult cancel Fiora’s ult if timed correctly

This answer is now out of date due to recent rework of Fiora. See here for updated information.

Yes, but only if Fiora has vision on Shen's ultimate location. The latest Rift Myths just answered this question for us: If Fiora uses her ultimate on Twisted Fate while he is channeling his ultimate will she teleport with him?

It turns out it is based on if you have visibility of where he is teleporting. The first test shows that Fiora will not move with TF if she does not have vision on his final location. The second test she does move because she has vision on the final location.

This also lines up with what Micheal Ayers tested with Nunu.

If Fiora targets a champion with her ultimate and that target becomes invisible/out of sight then the ultimate ends. You can see an example of this with Akali's shroud below: