Yes there are, though I'm not one of them. My understanding is that lactating after you've healed from piercing USUALLY isn't a problem (depending on number, size and placement of holes and peculiarites of individual internal anatomy).

Piercing after lactating I BELIEVE requires the woman to 'dry off' the breast involved and remain dry until the piercing(s) have healed, after which you're in the same situation as in the first paragraph.

If you're one of the few idiots who uses a leather punch to create your holes, your chances of successfully lactating afterwards drop dramatically.

redEva may be along shortly to correct or expand on this post.