I've had red wigglers living in pots I fed MC to. No. that's a line of bullshit perpetuated by the organic purists. And BTW, there is absolutely no difference between organic and mineral based nutrients in the soil. They are all the same to a plant. The few micro nutrients that need to be chelated for MC are done so using amino acids, which is what soil bacteria do to them and creates the same ionic form that the planst need.
Now ask about those "nasty chemicals" in manufactured nutrients. There are none.... NONE! I've asked every person who has ever said that to me to tell me the exact chemicals they are talking about, I've even emailed so called experts and asked, NO ONE ever has any kind of answer, because they are all just spouting heresay! Abut the worst thing might be EDTA, although even that is debatable as it's considered a food grade compound and it used as a preserative!