Obviously he wasn't the emperor, as the work was written under Augustus. Do we know much about this individual? Was there any relation to Antoninus?
We don't know, but the gens Aurelia was very populous in this time period and had several important branches. There would have been many "Marcī Aureliī" running around in Rome, and Vitruvius does not give us the cognomen (the third name) to help us identify the one he means. Some notable branches of the family are:
the Aurelius Cotta branch; there was a Lucius Aurelius Cotta who was consul in 74 BCE, and his son was called Marcus. This is a possible candidate. This branch of the family had consuls and other important members going back centuries.
The Aurelius Scaurus branch. There was a Marcus Aurelius Scaurus who was consul in 108 BCE and fought against the Cimbri. Cicero mentions one of his descendants, a Marcus Aurelius Scaurus who was a quaestor. He would be around the right age and rank to be with Vitruvius in Gaul under Caesar, perhaps as a legatus or somehow attached to the fabri.