Well, I'm not an expert either - I don't mean to give that impression ^^' I don't know, or I can't think of, any instance of it happening, but there must be leit motifs that are purely percussion.... But I suppose it'd have to be something pretty crazy in sound or pattern to be easy to identify.
...You know what? Nevermind, I just thought of a percussion-centered leit motif example XD : Akira's main theme (anime movie). It has drums as the center piece over a slow-building tonal base (voices), much like what you did here! ... Sure, the drums are mad; I guess that's why it's so rememberable... And it also helps that they are toned-drums, so there's a hint of a melody there. The tonal base (voices) also have a melodic line, not just tone... But the rhythm is undoubtly the main thing here.
Tl;dr : I have no idea how Akira soundtrack composer pulled it off, but yeah, it's do-able XD