Is the body of Saint Augustine of Hippo incorrupt?

No, Saint Augustine of Hippo's body is not incorrupt.

The Catholic Church makes no supernatural claims about incorruptibility. It is recognized that there are many possible natural causes for a body to not undergo decay. It may be considered during the canonization process but is not a deciding factor. If such were the case, then there are hundreds of natural mummies around the world who should be considered as saints, including many Inca burials in the Andes of South America.
When a body of a candidate for sainthood is discovered to be incorrupt during the canonization process, relics are usually removed and made available to the faithful for veneration. Thus, there are numerous relics available of St. Bernadette, Saint John Vianney, Saint Vincent de Paul and others.