Is it okay to use castor oil on warts when breastfeeding?

Yes, but won't work. Seborrheic keratoses sometimes go away when massaged twice a day with castor oil. They look warty but are not warts. Honest to goodness warts are caused by a virus and will not respond to castor oil. Try Mediplast tape on real warts. Generally works well.
Yes. Although I doubt it would do much.The general rule is all lotions /creams/oils you put on your skin cannot enter your blood and bother the formation of breast milk.