I don't believe that the name field or Secure Flight data in a reservation can accept an apostrophe. In fact, on a Sabre keyboard, the ' key is instead used for the ¥ symbol.

How does the name appear when the passport is swiped? If you look at the machine-readable zone on the bottom of the passport, does the name appear together or is there a < where the apostrophe should be? If it's all together, then it swipes as one word. If there's a <, then it swipes with a space in lieu of the apostrophe. Since the name on the Global Entry card and GOES account will be an exact match to the name on the passport, the name should be input into the reservation the same way it swipes on the passport to make sure that he gets Pre✓.

The name on the AAdvantage account technically doesn't matter since DHS uses the Secure Flight data to determine if Pre✓ will be granted.