They're only called Plantars warts if they are on the foot, especially the plantar or bottom surface. Otherwise they're just plain warts. According to DD's ped, there are over 300 viruses that can cause these.
There's a homeopathic/natural type remedy you can get by prescription called DDG. Its' sugar based adn comes from formulating pharmacies(one that make some of the meds on site). We used it directly on DS, when he was still nursing occasionally. Logic for the most part dictates that if you can use it on the child, nursing will be a non-issue. Most topical treatments are really not a problem either from what I've read.
Other means of treatment include freezing it off, using an acid product to burn it off--both done by doctor from my experience. There are prescription meds too, but those, despite my logic statement above, are pretty heavy duty. If I had a baby nursing, I might even put off using the one being put on DD's 3 days/week. There are OTC remedies too.
From the thread I started about DD's wart:
The duct tape treatment of putting a piece of duct tape on the wart.
Putting salt crushed aspirin under the tape are variations.
Putting a slice of fresh garlic on it. We've varied that by rubbing the freshly cut surface of the garlic clove on the wart.
TTO might help.
Visualization to get your body's own defenses to kick them off.
Oregano oil? If you find a source for this, let me know please.
None of the above seem to me to be problems while breastfeeding.