I do not have the answer to your question but I do know that in order to answer this question you must know all of the kashrus related responsibilities the OU fulfills and which of them are taken over by the other hechsher.
The ingredients of an item is not the only criterion required to make something kosher.
I think that this question might be assuming an oversimplified view of the enormous system required to ensure that something comes out kosher from start to finish.
Just to make it clear, I am embarrassingly under-educated in this arena and would love to hear people's input. I am just cautions of people seeing one piece of the entire system, taking it out of context and judging it based on a position that is both ignorant of the halachos and the system that any given agency has in place.