I’ve got wrought iron barrels I shoot. They don’t season. They are not porous and I don’t think cast iron is either. The seasoning of a cast iron skillet sits on top of the iron which is often poorly finished. There is much mythology about wrought iron, cast iron, and “modern steels”, most of it old wives tales.
You can take mild steel, tool steel, or wrought iron, stick it in the coals, take it out and brush it with linseed oil, corn oil, lard, chicken fat, possum fat, or whatever type of oil that cooks to a polymer when overheated, and regardless of whether mild steel, high carbon steel, or wrought iron, will all develop a “seasoned” finish. Try it.