Will rubbing rosemary essential oil on your stomach really induce a miscarriage?

No . Herbal treatments to induce miscarriage do not work reliably enough well to be used, and i don't know what kinds of side effects it could cause.
Probably not but... By definition, "alternative" is different than modern western medicine. Generally any drug, herb, treatment, or oil that stands up to rigorous scientific scrutiny is included in modern medicine. Many alternative practices, oils etc do not stand up to scientific scrutiny and cannot be shown to work.nor safe. Some could do serious harm. Check https://nccih.nih.gov/ for research.