I'm sure there would be confirmation on that by now but I can't say much since I aint tried or researched into it, other than that, The shiny versions are absolutely awesome.
I've been reading mixed views, I've seen some people saying they are and others that they aren't.
Latias/Latios from the story are apparently not Shiny locked, along with the other Legendaries you get on the mirage islands etc being non locked either.
Although I'm unsure about Groudon and Kyogre either, I bet Rayquaza is Shiny locked though.
Nobody has been able to successfully reset for a shiny so far, so it would appear they are shiny locked. I have been looking around for a while to see if somebody got a shiny version by soft resetting, and even with people having Shiny Charms to help them out, Groudon and Kyogre just don't seem to turn shiny.
I think it would also be shiny locked since it is still part of the main storyline. Also Serebii states that as of now, they are Shiny locked. It's still under testing though.