> Also I assume radar-proof is just because it's a ground effect vehicle that will never fly high enough to show up on radar

My guess is yes. Simply because the Caspian Sea Monster [1] was "the largest and heaviest aircraft in the world from 1966 to 1988", not at all stealthy looking, and simultaneously also "undetectable to many radar systems, as it flew below the minimum altitude of detection."

So yes, a much smaller craft will also be hard to radar. Notwithstanding that the tech has moved on at both the "detect" and "don't be detected" ends of the contest.

As I understand it, it's also easier and safer to fly these craft now, as they are computer-stabilised, which the 1960s design could not have been. And therefore easier and safer to fly them lower. (The Caspian Sea Monster "was destroyed following a crash caused by pilot error." )

1) https://en.wikipedia.org/wiki/Caspian_Sea_Monster