There are rules for Cypher and a bad Formation of him and CSM Chosen that you should avoid, but he can NOT ally with Dark Angels. It is not allowed, so if you want to make an army of Fallen, you choose CSM or vanilla Space Marines (or any other Armies of the Imperium but DA) and include Cypher as an HQ choice. And he currently can be used with Grey Knights and Sisters just fine. But, he is getting a new model and new rules in very little time, like a month or two, so your best choice is to sit tight and see what you do with him once he gets some decent attention.
If you ask me, a Forge World Chapter like Raptors or Astral Claws are great choices. Astral Claws get Bike skills and Stubborn, like a discount version of Dark Angels already, so they might be the closest you can get. Use their rules and make them look however you want.