Worm castings is simply dirt that red worms lived in. The worms break down organic matter into compost. Worm castings are low in Nitrogen and not very rich in anything else. Worms or worm castings alone will not nearly supply the necessary amount of food to sustain the plant. Mostly, castings are used to increase drainage in the soil.
The only other benefit I can see of adding worms directly to your soil is that they will aerate the soil. Also, worms need food too. So unless your adding organic waste to your soil they will not survive very long. Thats why the worms belong in the compost pile, not in your potted plants. In any case, they won't hurt the plant.
I figured they would need to feed anyways, but just wanted to check. Good thing I didnt get some bait worms and toss them in my soil.
I actually mixed down 2 diffrent ferts to hit my vegging babies with. My compost pile started today with all the side cuttings from a large salad and the fruit from breakfast this morning that was left over and removed. Dog Doo too apparently. All animal feces is supposed to be supplemental...
Earthworms will not survive in a medium used to grow cannabis as the acid salts kills them. Earthworms need a neutral or slightly alkaline soil to live. That is one reason why you never put citrus peels into compost - they are too acidic. Also, worm castings are usually neutral ph, or slightly alkaline and will need ph correction for cannabis.