All of the above. Scratch and Mealworms are both treats, should not exceed 10% of the daily diet, as both are nutritionally imbalanced. Typically used as an enhancement/enrichment activity, not because it improves their feed (quite the reverse, actually), but to provide entertainment (to you, in part) and to encourage certain behaviors - like digging/scratching to seek food.
"Scratch" traditionally is a high percentage corn mix (because its cheap, readily available, stores well) often with some amount of seeds or additional grains mixed in (milo, millet, boss). End result is a high energy, low protein, imbalanced amino acid profile feed - like you trying to live on plain white bread or white rice which has NOT been enriched.
"Mealworms" are animal protein, and a decent amount of it. Its both balanced, and much higher protein% than most owners feed their flock. Often fed either as a treat, or as a buffer when a bird is experiencing protein stress (such as during a severe or prolonged molt). Unfortunately, mealworms can be as much as 15% fat (live) and 40% fat (dried). Since the target for fat as a percentage of total daily feed is usually given around 3.5% +/-, you can imagine how quickly excess fat from mealworms can begin to accumulate in your birds, contributing to fatty liver disease and the like.
BOSS are similar, in that they are high protein, high fat, but as a plant, rather than animal, protein source, the amino acid profile is less than optimal. They are also quite high in fiber, which has its own issues. Stripped of the shell, they are less protein and more fat than a comparable weight of the typical dried mealworm.
Better, I find, to offer a higher protein, nutritionally complete diet year round, instead of trying to "fix" a commercial feed on the farm, by hand, trusting that you are measuring correctly and the birds are partaking equally. That's generally not the reality.
Hope that helps, though I've really said nothing the others above haven't either said or alluded to.
