There ia an Angels of Repentance chapter mentioned in Chapter approved and the Index Astartes article on Space Marine chapter names.
A Chapter's name might embody the character of the Chapter (such as the Blood Drinkers), the world of thier founding (Praetors of Orpheus) or the Legion gene-seed from which they derived (such as the Storm Lords and Marauders)
So it could literally be Angels from Repentance.
Or as Murray145 says they do sound very much like a Dark Angels successor.
They are not listed as being a 2nd founding Chapter of the Dark Angels however and as far as I recall the High Lords of Terra restricted use of the Dark Angels geneseed.