Shiny chances as a raid reward?

Not from my experience. I’ve yet to encounter one (outside of legendaries) from a raid.

Took me 31 Absol raids to get a shiny...but still no shiny Swablu. I think the answer is: Maybe + depends.

Absol, Mawile and legedaries have a higher rate. The rest probably have the same rate as in the wild.
https://thesilphroad.com/science/pokemon-go-shiny-raid-bosses-community-day-rate/