A lot of the special effect CGI models were taken directly from assets made for Halo 4's own in-game cutscenes. This can lead to some minor Continuity Snarls if a viewer is being picky.
Cadmon's ODST armor (along with other ODSTs shown) is reused from the live-action short "The Life", also known as the "We Are ODST" commercial for Halo 3: ODST.
The armor worn by Kelly-087 and Fred-104 are modifications of the armor worn for the Halo: Reach "Deliver Hope" commercial. Amusingly enough, one of the helmet's modifications was attaching the prop of an armored knee plate over the bottom of the visor.note (HaloCosplay enthusiasts had quite a chuckle when they saw the helmet◊.)
All the Warthogs shown are the same prop with different modifications. Said prop Warthog is a fully functional vehicle originally made by WETA for the long-abandoned Halo film. It was also used in the Neill Blomkamp-directed Halo 3 promotional short "Landfall".