It mostly comes down to if you know how to rng tbh as well to know what truly can be shiny match with nature with 4th gen and below games which bold 6 iv. I am pretty sure a 6 iv bold would be a hack because that spread doesn't exist in the game program for heartgold and soulsilver, its been awhile since I rnged though on 4th gen in general which someone correct me if I am wrong that rngs 4th gen but your spot on the money for unova and 6th gen though
For encounter RNG, no. Only Modest, Timid, Docile (pff) and Calm can be IV 31 all in Generation IV. Shiniess is easy if you know what nature + IV spread you're going for.
For breeding, any nature is possible with ANY IV spread.