So, yes, the Aikikai Honbu can award a "shihan" certificate. However, as I understand it, that "shihan" status is *only* granted within that one organization. It does not cover the Aikikai or other organizations.
That brings up an interesting question then- what if a person who gain shihan status in his/her organization (not Hombu) later leaves that organization? Is there such a thing as a non-Japanese "independent" shihan?