That's what this is called when a writer "self-publishes" a book no one else will publish. In this case, the publisher is gathering a bunch of images from photographers who probably don't have enough images or name recognition to get published on their own, and compliling them into a book. If you think the exposure in that book is worth it to you, then go ahead. Just make sure, as you have, you've registered the copyright, and that the published includes full photo credit and contact info somewhere in the book. For example, the appendix might have contact info (website, email, address) for all the photograpehers with a reference back to which images were their's.
There's really nothing wrong with this if you know what it is, going in to it, and you're OK with that, but most of the time the publisher gives the contributors at least one copy of the book. I've done this a few times when an actress wanted to use one of my shots along with a hundred or so others, and we all got a book (paying each photographer up front, for what would likely be a minimally selling book, would be prohibitive in today's publishing world). There are a famous series of photo books called called "Day in the Life of..." by photographer turned publisher Rick Smolan, where he coordinated photographers around the world shooting simultaneous events over a 24 hour period and stuff like that. Anyway, in one of his latest books, he did exactly what you're doing - he got all these photographers - famous or not - to send him photos along a particular theme, for free, to be published. And they did it, and it was.
Also, many professional photographers actually pay big money to get into what are called "source books". They essentially buy a page or two for anywhere from $2500/page and up, plus design expenses, and the publisher delivers free copies to graphic designers and ad agencies all over the world. There used to be a lot more, but the two big ones remaining are http://www.blackbook.com/
Of course they've also gone "online" in the last few years, but you can still see the main books in print. Many photographers buy them at camera and art stores to use for inspiration.
One last thing - when you registered this image, I hope you didn't just register THIS image, but rather take advantage of the ability to register a lot of images at one time on a CD? You could/should have registered everything you shot that day/week/month/year on one CD for one fee, and you'd be covered on all of it.
Andy Pearlman Studio