Most likely. I can't throw around facts but with what we have available to us I can assume he is. 2 major things that are tied into him are: 1. What the cryptarch says. That whole Oryx-Dead King. 3 syllables. Nine bursts. Osiris. This kind of makes me want to assume that whenever we see Oryx (many assume he is the taken king in the upcoming Comet DLC) that Osiris will show up as well. 2. The disciples of Osiris and the trials. I feel they wouldn't have just thrown in the disciples and Osiris just for fun. There is definitely more to Osiris but right now he seems to be the biggest Character in the Destiny universe as he has impacted many things. Also, if you read the fate of all fools bounty steps, it almost feels as if you are being told the steps by Osiris. Just a neat little tidbit.

Maybe the Lighthouse is Osiris' hideout?

Maybe. I haven't been there but I have heard some area is blocked off.

I'm wondering when they will introduce the Fate of al Fools, I am guessing the same week as E3.