The answers to all of these questions are best asked by your former coworker of his (your?) former travel contact. If you still work there and give the wrong advice and he winds up giving you up, ask yourself how you come out of all of this.
Before starting down the technical discussion, how much are we talking here and is it worth it? Sometimes a bit of common sense goes a long way. $50 or $5,000?
Depending on your employer's ticketing deal with AA, it may well have the ability to apply credits to other employees despite what people experience with their standard ticketing rules (and despite the mistaken view that this is a contract of adhesion which it is not and simply shows a lack of understanding of the term).
If the employer has the ability to move credits around, it may already have done so, may still do so, and certainly does not need to consult with your former coworker to do so. Also, depending on the corporate TA it uses, it may well receive reports of how these credits are used just as it receives reports of all changes made to tickets it initially pays for. While many employers could care less, others care a lot.
At a more granular level, the above note is entirely correct that if your former coworker converts the business expense to a personal benefit, that is income and he will need to report it. By the time he pays federal, state, and any other taxes on that income, and goes through the hassle of doing so, we go back to the practical question at the beginning.
That's why this is all something where the nicest thing you can do is throw your hands up and say that it's really all too complex and he ought to call the travel people who will presumably tell him. If he is afraid to do that, presumably he knows the answer.