Can I use my Dark Angels with my Space Wolves?
Yes you can.  Wolves and Dark Angels are qualified as "Allies of Convenience" under the 6th edition allies rules.  This allows you to field 1 HQ, 0-1 Elites. 1-2 Troops, 0-1 Fast Attack, and 0-1 Heavy Support options from the Dark Angels codex with your Space Wolves detachment.

In game-play rules they are treated as enemy models that cannot be directly target by your weapons and abilities.  The DA troop options do count as scoring units for you though.