Or at least it does on Nexus Blitz. We won a late game snowball fight, got GA's for the team, and decided to take a 5v5 teamfight. Pyke proceeded to get 4 kills with his ult that teamfight because, mysteriously, his ult would bypass GA and give him the kill anyway.
If you can get a replay of this or recreate it, that would be most helpful, Nexus Blitz is still in Alpha & has plenty of Bugs lurking about.
I believe that the issue is that the 90 second Guardian Angel might not be coded the same way as Normal Guardian Angel is since it's a buff & not an item passive. This would explain why Pyke
can ignore it using his Ultimate [R: Death from Below]. Given the circumstances, Urgots 
Ultimate [R: Fear Beyond Death] might also be another one to consider since he can execute you too.
