The way that HubPages works is that the article you write is the content users are searching for. So if you posted a hub in the 'free ebook' section of HP, then it might get flagged as overly promotional since its sole purpose is to point the user in a different direction. However, you can create amazon capsules to your book, you just have to make sure that the hub has a purpose without it.
Some examples of hubs you could include a link to your book on would be "Top 10 free kindle books", "How to write a novel", or "How to publish on Kindle". You can also commission a separate HP writer to write a review of your book as a hub.