Boulton isn't the head of the UN
Geez, can't you get anything straight? Boulton is now the US ambassador to the UN. The head of the UN is still Kofi Anon.
Recess appointments are specified in paragraph 2 of the 17th Amendment. It wouldn't have been necessary had the Senate given him a simple up or down vote. Many presidents have used recess appointments (including Clinton). They're fully constitutional and temporary - Boulton's term will expire when the next Congress takes office in January, 2007.