I think we should make a distinction between a game's engine and format. Correct me if I'm wrong, but from what I understand, Xill was referring to RPGM's visualisation and mechanics, with top down view and relatively free (animated) exploration of areas, including jump-and-run elements + D&D battle stages, as opposed to Ren'Py stylistics, which more often than not consists of still backgrounds with clickable areas, multi-layered paperdolls, textual choices and sometimes mini-games, which is basically an enhanced VN.
There are Unity games in RPGM style, 'Third Crisis' for example. And I am sure there are Unity games in Ren'Py style.