Well, Valve is planning to replace Steam Greenlight with Steam Direct this Spring so even if they're able to put it on Greenlight, it's probably better to wait as Greenligting takes time (and 100$) and they may not be able to make it before Steam Direct comes out.
Yeah I talked to a Steam guy a week or two ago (I'm working on a few games and had a Greenlight question). They're going to replace it with Direct but for now the process is still Greenlight as they haven't worked out the details yet on Direct (like cost). No idea if the Raft developers will just wait for Direct or go through Greenlight right now (but given the popularity of Raft I'm sure it would go through quickly).