It in not true that just japanese can become shihan.
As a proof I can testemony that here in Brazil the organization that I belong the Brazil Aikikai Confederation itīs technical director, Wagner Bull Sensei , in last january, received the title of Shihan issued by Aikikai Hombu Dojo and I saw the paper. Anyone interested to see the certificate can look and the link :
http://www.aikikai.org.br/wagner.html
Joacir Junior