I'm talking specifically about spirit rend which for a hit goes: 3d6+ intelligence modifier damage(save ends). If the target is undead, it takes no damage and is not immobilized. Instead, the target must take a free action to move as far as its speed allows to a square farther away from you, and it is dazed(save ends). One of my PCs used it on his own team member (who was a revenant to try and get him out of a sticky situation. Wondering what should have happened. (let him move away).
He would be moved away.
But only if his Wizard fellow considers him an enemy... (see the Target entry for the Spirit RendDDI power).
The RevenantDDI is, in fact, considered an undead creature because of its Undead trait:
Undead: You are considered an undead creature for the purpose of effects that relate to the undead keyword. You are also considered a living creature.
Living Dead: Because your soul is tainted by undeath, you are both living and undead. If a power has different effects on living creatures and undead creatures, you choose which effect applies to you.
So, while revenants are both undead and living creatures, vrylokas are either one or the other.