Yes. Elsewhere they say it explicitly: all the yield is expected to come from the basis trade - nothing riskier than that. I lost the link and can't find it right now, but it confirms what you're saying.

I wouldn't mind throwing some corn at a thing like that, especially if the custodian is "too big to fail", as Coinbase got to be. As for nonavailability in the US, this is exactly the kind of thing that might change with a friendlier regulator at work. And I'm pretty sure there will be copycats and similar funds will pop up like mushrooms. Trusting the custodian will be the hard bit. But yield without selling is sooooo sweeeet...