So not hacks. Whenever you do a raid, the pokemon you catch has a ton of information about its den stored in it. When you put a starpiece in a den, it generates hundreds of thousands of possible mons in the den, all with chances to be shiny. Each mon is separated by a day, or a “frame.” If you catch a gible in a den, you can use that gible to check when the den will havw a shiny; how many frames away. The stats, nature, ability, everything comes up for every single frame.
A host takes that information, and skips each day/frame until they get to the shiny one. It’s all rng manipulation, and it sometimes can take over a week.
No hacks required, the only thing hack related is the use of bots that can take apart the pokemon’s information from the den and give it to you, but all you’re doing is reading the information a pokemon already has in it, not adding or changing anything.