[quote=@Thundercrash]
The idea here looks interesting. Question: suppose I make a character based on Groudon. Can I integrate his Primal form? And the moves that I give him ones that Groudon can legitimately learn in game, or can I choose other moves?
[/quote]

The max starting level for any Legendary here is 30, and If I am correct Groudon doesn't know any of his Primal moves till later on.
That being said, Groudon/Kyogre require their orbs to 'evolve' or rather primal reversion, and these are items you wouldn't start out in this roleplay with, but can be gained at a later date.
So from my understanding that's a no to start with; they could be acquired later on though.