I don't think that they should have any problems with the law. They aren't scanning only books, but also business documents, business cards, photos and greeting cards. Since they intend to work with business documents, they must be able to assure the customer that they won't be keeping a copy of said documents.
When it comes to books, there are two possible cases: books that are available in digital format, and books that aren't. I don't really see how it can be advantageous to use this for normal books available as ebooks (300+ pages on average) unless the ebook costs more than the pbook. It costs $4 + shipping to get a pdf of the book plus the time to send the book and the time it takes them to digitize it. Maybe if you buy second hand books and get this done but it still might go to $10 per book and a week of waiting to get a pdf.
I can see the system being useful for books that aren't in digital format, and then the customer loses the paper version (unless they want the remains of the book returned, but that would likely cost more).