Just like how black floral powder from botania and ink sacs can dye sheep, I feel like Iron gall ink and the other substitutes should also be able to dye sheep

do note that the iron gall ink is meant as another option if you cannot find squids, it's not ink. (also dont think u can just apply a iron nugget that has black coating onto a sheep). If you really needed black wool either use the iron gall ink (which is quite cheap to make) or just search for squids

No no Small, currently Iron Gall Ink can't be used to dye sheep. This could actually be a good minor feature to add.