Much like the Oblivion Ring and Emrakul trickiness of Standard long past, this question deals with a common misunderstanding about when Oblivion Ring and Detention Sphere actually target. While you can cast Redirect on any spell at all, it won’t actually DO anything unless that spell has targets for you to change. And neither Oblivion Ring nor its cousin Detention Sphere actually target anything as spells; only their triggers target.