I agree that Graven Embrace is a far cry from Feign Death/Death Peace and is mostly useless.
As far as re-aggroing the mobs once you're down for the (five second) count, if you pull the mobs far enough away from their bind, you can stand right back up without re-aggroing them, even if they're right next to you. Have you ever been standing near someone who pulled a train your way, died in front of you, but you didn't aggro their mobs? It's the same premise.
One odd thing, however, I hit Graven Embrace near Nektropos Castle, well away from an angry train of zombies that were chasing me. After I hit the dirt they kept coming and beat me further into the ground once they caught up. Perhaps this spell is not recognizable by undead as they can sniff out the living? Odd, at any rate.