I voted "no." I would have voted a large, resounding "No!" but that wasn't an option.
It seems to me that the onus is on the "yes" people to prove their side, due to the nature of the question. So, I ask those who voted yes (so far the overwhelming majority):
What items can you learn only by teaching aikido?
Why are those necessary to achieve "an advanced level" in aikido?
I do think that teaching certainly helps learning aikido, but I can't think of anything that you learn by teaching that is both necessary to a high level of skill (which is how I read "an advanced level") and impossible to learn any other way.
So far the two things suggested are responsibility and being an effective communicator. I don't think the first can only be learned through teaching. Being a higher level student should bring the same sort of need to be a model. For the latter, I don't think that it's part of being highly skilled in aikido or that it can only be learned by teaching.