Loki's Blessing clan upgrade in Yggdrasil during a game of Blood Rage
Yes.

From the FAQ:


  Q. May Yggdrasil be invaded if I lose a battle using Loki’s Blessing (allows
  warrior to invade without cost the province where the battle was lost)?
  
  A. Yes, Loki’s Blessing allows you put a Warrior in Yggdrasil.