Accepted answer: no
There are some effects in the game which remove a champion's sprite from the map, rendering them untargetable for a moment, such as Elise's Rappel. Does the Summoner Spell Flash do this as well, even just for a split second? Or is the champion always on the field and targettable at all times? In other words, does Flash instantly place the champion at the target location such that there is no moment in time where the champion isn't on the map, or is there a moment when he doesn't exist on the map?
I ask because I was playing a game where I was getting double ulted by both Nunu and Morgana. My Flash was up, but it wasn't enough to escape the range of their ultimates completely. I am wondering whether, if I timed my Flash just right, if I could make myself untargettable for a split second and avoid the effects of one or both of the ultimates when they triggered (i.e., Morgana's stun activated or Nunu's ultimate blew up for tons of damage).