Shortly after my previous post, I received a message from a representative from R.R. Bowker, which is, of course, the the agency that distributes ISBNs in the U.S. In short, he provided some very useful information, including a link (Click here) of all the Bowker-authorized companies. Lulu is definitely one of them.
This, of course, tells me a couple of things. First, and most importantly, regardless of the option (in this case being selecting the Published By Lulu service), I made the right choice by sticking with Lulu. Secondly, folks are actually reading this thing!
So, thanks to Bowker for the information, and I hope to hear even more in the future!