I haven't done a lot of heavy digging into Osiris. He has a brief mention in the mission card, but for the most part he is simply mentioned in item descriptions. But, what I know is he was a warlock who became obsessed with the darkness and specifically the Vex. After being consumed by this obsession he was exiled. He tried doing things such as crafting armor from pieces of Vex. He built guns. I think that the possible connection of Osiris to the House of Wolves is that if you want to do illicit things and hide from the Vanguard, the Reef seems like a good place to hide. It is very possible that Osiris is hiding in the Reef while he studies the Darkness.