I finally unpacked Darkvein and figured this out the hard way too. It's a shame! I reported this to the hearthstone bug report to see if it can be fixed.
My new updated list:
### darkvein
# Class: Warlock
# Format: Wild
#
# 2x (1) Altar of Fire
# 2x (1) Curse of Agony
# 2x (1) Plague of Flames
# 2x (1) Touch of the Nathrezim
# 2x (1) Wicked Shipment
# 2x (2) Defile
# 2x (2) Drain Soul
# 1x (2) Plot Twist
# 2x (3) Backfire
# 1x (3) Brann Bronzebeard
# 2x (3) Free Admission
# 1x (3) Tamsin Roame
# 2x (4) Bloodbloom
# 1x (4) Tamsin's Phylactery
# 1x (5) Lady Darkvein
# 2x (5) Runed Mithril Rod
# 1x (6) Dreadlich Tamsin
# 2x (8) Void Contract
#
AAEBAarABAbamwPy7QOwkQTxkQSY1ASH6gQMkMcC58sC1IYDnakDld4Dk+QD6+0DvfEDg/sDxYAE56AE/KwEAA==
#
# To use this deck, copy it to your clipboard and create a new deck in Hearthstone
2
It doesn't work. The phylactery doesn't discover the Darkvein adds (doesn't recognize them as "Deathrattle minions"). Not sure if a bug or by intention.
2
Siamat seems like the perfect replacement.