They use DAZ to make the renders
Ren'Py makes the VN where you can have text and backgrounds and choices and start animations and show pictures etc etc
Some other people use other programs to make renders / images but none of them use RenPy for making them.
Just for your information (FYI)
Whatever begets renders in the
Radiant style of
Radiant characters, with or without background settings, will do nicely.
I am aware of several VN render-styles. So what ? I doubt many members here are wishing for
Radiant to be redone in Honey Select or Affect 3d, for example.
Just an attempt to locate the assets that were used to make
Radiant models. Then, hopefully, an attempt to render
Radiant personalities in erotic poses.
The official
Radiant wallpapers that have been seen in this thread are meh. Surely, someone can take the erotica factor up a few levels.