Sister of the Thorn, Grail Knight, Warrior Priest of Sigmar have no unlockable hero skins for completing all of Helmgart on Champion and Legendary difficulties, as opposed to all other careers. They don’t have unlockable headwear for completing 100+ games on Champion or above with them, either. This is an issue, and should be remedied.
Most of the DLC classes have a black “legend” skin obtainable in their cometic upgrade DLCs. Some have a red “champion” skin as well however GK and WP seem to lack this skin. WP and SOTT get their skins without having to complete challenges however GK and OE have different challenges to unlock their skins. GK does have a complete 100 games on Champion or above for his alternate hat, but he is the only DLC class to have this challenge.