There are no heralds in the Furnace of Pain. Pit Lords there cannot ever spawn as heralds because Furnace of Pain can't be a Terror Zone (not even with an act 5 Worldstone shard)
What if you open Furnace of Pain prior to Terrorizing Act 5 ?
In another topic someone said it might be the way to get Cows TZ when Sharding A1,
I'm thinking the same for Ubers mini bosses (and even Uber Trist ?)
Seems normal that it wouldnt work but who tried yet?