Unless otherwise prohibited by the bylaws, a person can usually hold more than one office in a nonprofit organization.  It is not unusual in a small organization for the same person to serve as both secretary and treasurer, for example.  It is also not unusual to have vacancies in officers, particularly for a vice president who does not have much to do.  I have never heard of a dual officer asserting a right to two votes because of the dual office.  Unless the bylaws clearly state that each officer will have one vote on the Executive Committee, I would rely on the more general principle that each person has one vote (without regard to the number of positions such person holds).  If it becomes contentious, it may be appropriate to spell out clearly in the bylaws what you intend.