Don't know - couldn't find it anywhere. Since the ferrata follows an old climbing route, most likely the dude who climbed it first was called Hohl. On the other hand, Hohlweg, the direct German translation is mor like a "hollow road", used for deep cut roads. However, I don't really see a connection here.
"Got tight last night on absinthe and did knife tricks. Great success shooting the knife into the piano. The woodworms are so bad and eat hell out of all furniture that you can always claim the woodworms did it."