does this make it illegal?
The disclaimer is to make it clear that while GS Games IS aware of this project, they have not commissioned it and are not involved in it. Note that the community SU port project was specifically referenced in the GS Games twitch stream podcast a few days ago. Smokeshank pretty much figures that, like similar efforts before this one, it won't go anywhere... (Challenge accepted?). We aren't monetizing this and have no plans to monetize it, it's just a community effort, for free.
It's a community effort to explore different approaches r.e. how SU Unity handles things. SR7 likes Fungus a lot, and is comfortable with how it works, and I imagine that GS Games prefers Unity for SU at this point, but Ren'Py introduces a number of other options, such as easier moddability.
There are those among the 'community build team' that hope that an 'official' Ren'Py version of SU becomes a thing someday, seeing that the current versions of SU Unity have so many weird bugs, and perhaps this might inspire the GS Games team to shift gears, but in the meantime, yeah the community effort is mostly 'just for fun'.
And you DO realize that this is a buccaneer forum, right?