Yeah, the pigs will definitely eat the critters, too, but going through a critter will significantly reduce the amount of feed. The conversion of DM manure to DM earthworm is 10:1 (or less). Earthworms are mostly
water. That means the pig is getting 1/10 of the feed value of the original manure. Grubs are around 6 or 5:1. Then there's the conversion through the bacteria and other critters to get it to earthworm/grub food in the first place. Going through bugs increases the protein, and that is good for the pigs too, so the best way is to get some insects and some manure/plant matter together.
Many manures start out high in protein, already. Rabbit manure is 20% or better. Pigs love poultry manures, too.