An employer may keep lists of individuals who are ineligible for rehire, so long as the reason they are ineligible for rehire is not discriminatory. However, if an employer refuses to hire individuals it reasonably believes engaged in theft, that is their right to do so.
Of course an employer can keep a list of employees it would never hire again. If you ran a business wouldn't you want a quick list to compare future applications to so as to determine if you already dealt with that employee? Not only is it not unlawful, it is a good, prudent business practice.
That does not mean an employer can put someone on the list simply because they are a member of a protected class of people or because they had engaged in protected conduct. However, anyone could be put on that list for any other reason, or even for no reason at all, or even an erroneous reason, and the employer is acting lawfully.
The last sentence of your post makes no sense and appears out of context. However, if what you are saying is that the person was placed on the list because they successfully prosecuted their rights under the ADA, then that would be unlawful. Given the loss of money, good luck proving that was the reason the name got on the list.
Good luck to you.
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