I'm pretty sure it is shiny locked, but I see a lot of Shiny Victinis. Are they hacked?
Victini has never been given out shiny, and every event since Gen V has either been shinylocked or guaranteed shiny, so yes, it is impossible to get shiny Victini without hacking.
Yes, they are hacked since shiny Victini has never been released in any country, plus it's shiny locked, as you mentioned.
all those shiny victini you see could be hacked... or could be from wondertrade. take for example, pokenursery. he gives out shiny locked Pokemon like shiny meloetta and shiny victini. that's the path i'm going for. and these lucky people won a shiny victini from wondertrade