To what extent can OWS and ultra-lefty pundits like Glenn Greenwald be considered Democratic party actors?That's a great question, and I'd like to spend a bit of time with it, beyond giving the most basic answer, which is: tough question.
OK, first. The formulation "party actors" is something that I've actually started using only recently. For me, it's a shorthand way of referring to everyone who is more active in the party than just plain voting. So it includes formal party officials and staff, candidates and elected officials, campaign and governing professionals, activists, donors, party-aligned interested groups, the partisan press, and perhaps more. Of course some are more involved with the party than others, and many (most?) have mixed status and mixed incentives. So a pollster -- one of those "campaign professionals" -- may be a party actor but is also running a small business, with all the profit incentives that go with that.
We need that because looking at only formal party organizations (the RNC, the DCCC, the Maricopa County Republican Party) clearly misses important things that are going on that are clearly party activity. If the US had membership parties in which everything done by the party was a function of what those members did, or perhaps all that mattered was what the party bureaucracy did, then this would be a lot simpler. But the real world of US parties is (organizationally) messy, and so we need to account for it.
The question is where the boundaries are, and this is where the question of someone such as Greenwald is interesting. I guess I'd look at a couple of things. One is simply self-identification: does an activist or a member of the press think of himself as a party member? But that's not good enough, because very few people read my stuff or Seth Masket's stuff or Cohen et al. or Casey Dominguez or any of the other party network scholars, and the press often misreports all of it, and at any rate one of the weakest portions of US contemporary parties is in the areas of ritual and their place in the popular political culture...the bottom line is that a lot of people out there sure appear to be partisans despite claiming that they are not. And so in addition to self-identification, we need behavior: if you act as if you are a party member, then that's strong evidence that you probably are one. And that's an empirical question, but often a difficult one to answer. Does someone wind up always supporting one party? Does she attempt to affect the course of that party (but not, really, the other one)? Does she mostly (when it comes to politics) speak with people from that party? As far as I'm concerned, there's no clear test that says "in" or "out" of a party, either for individuals or for groups, but put all of that together and you can get a fairly good sense of it.
So I'm not really going to answer the question, but that's the way I'd think about answering it.