Hintergnomes don't exist. Well, they must exist, they make the hinterpockets, but nobody's ever seen one. No one knows what they are, and the Hintergnomes assure everyone else that they aren't real. If they were to exist, only the people of Unda would know anything about them, and the Undafolk aren't spilling any beans (or telling any tales).
If the Hintergnomes did exist, hypothetically, they'd be excellent mushroom tenders (as well as apparent masters of time and space), and would maybe even be responsible for a majority of the food supply in Unda. Unfortunately, as the Hintergnomes don't exist, this can't be the case.