Herman Cain is saying that, if elected President, he would require all Muslims who might be working in his administration to take loyalty oaths swearing that they would not let their religious beliefs influence the conduct of their jobs. However, Catholics and Mormons would be exempt from similar oaths since he already knows that their beliefs would not present problems for him (he was not asked about Jews, Protestants or other religions)(for the record, Herman Cain belongs the the National Baptist church, the largest African-American Protestant denomination in the US).
http://thinkprogress.org/politics/2011/06/08/240415/herman-cain-require-muslim-appointees-loyalty-oath/