More on the Vice Presidency and the Executive Branch:
Recent revelations that the Office of the Vice President is not in the Executive Branch brought me to read the government's brief filed in Cheney v. United States District Court, the 2004 Supreme Court case on whether a civil suit could force disclosure of meetings held by the Vice-President to advise the President on energy policy.

  The brief, filed on behalf of the Vice President, argued:
Any attempt by Congress to regulate the President's ability to obtain advice from officials in the Executive Branch would unconstitutionally interfere with powers expressly reserved to the President by the Constitution. See, e.g., U.S. Const. Art. II, § 2, Cl. 1 ("The President *** may require the Opinion, in writing, of the principal Officer in each of the executive Departments, upon any Subject relating to the Duties of their respective Offices.) . . .

During the Constitutional Convention of 1787, the Framers considered several times whether to provide the President with some form of advisory council that included representatives of the Legislature or Judiciary. See James Madison, Notes of Debates in the Federal Convention of 1787, at 487-488, 509-510, 569, 598-602 (W.W. Norton & Co. 1966) (debates of Aug. 20, 22, and 31 and Sept. 7, 1787). Each such proposal was rejected. The Framers chose instead to enshrine in Article II the President's power to seek advice from those under his direct control. As Alexander Hamilton subsequently explained, the unity of the Executive would be destroyed if the President were "subject[ed] in whole or in part to the controul and co-operation of others, in the capacity of counsellors to him.” The Federalist, No. 70, at 472-473 (Alexander Hamilton) (Jacob E. Cooke ed., Wesleyan Univ. Press 1961). The Opinion Clause thus explicitly confirms the President's authority to gather information and opinions from his subordinates. The history of that provision, the structure of Article II, and the obvious constraints of the separation of powers make it clear that the President's authority to receive opinions from Executive officers is not subject to interference from or control by the other Branches.
Seems like a strange point to make if the OVP isn't in the Executive branch.