The Wulfen are inspired a little by the new Orruk Brutes in that they have mixed weaponry like crazy. These guys make up the foot troops of the newly minted "Fenryka" faction of Astartes. I imagine that they would work as their own faction with Wulfen and Thunderwolves making up the massed units and the Wolf Lord at the fore. They've even got their own Psyker (the Rune Priest), so they really have everything a faction needs. By renaming them Fenryka, they're also able to work for successor chapters (not that the Wolves have many of those).
Similarly, the Blood Angels are now "Sanguine Astartes". What they lacked was a leader, so I added the Sanguinor. Even though he was a special character, I feel like the proper Sanguinor model or Astorath or just some cool looking dude with a jump pack and a big sword could do the trick quite nicely. This guy is really just a beatstick character with a pretty cool command ability, and he rounds out the faction. So Sanguine Astartes now has a leader, a psyker dreadnaught, and two units of their own (Sangunary Guard and Death Company) to round out a proper faction.
Of course all this isn't to say you can't mix them with plain old Imperium Astartes, it's just that they have some fun internal synergy now.