Since Groudon is Shiny-locked in ORAS, I'd have to get a Shiny Groudon from an earlier gen game and transfer it to ORAS. I want to know if it is possible to teach Precipice Blades to this Shiny Groudon.
Yes it would.
All you have to do is Level it up to lvl 45 and it will learn Preipice Blades
If your Groudon is already past lvl 45 then use a Heart Scale
Hope I Helped!
Yes, you can get Precipice Blades on a non-native Groudon. P-Blades was simply added to Groudon's movepool, meaning yours will either learn it via level-up, or you will be able to re-learn it with a Heart Scale.