Apparently the drivers are bundled with the OpenNI download. I've successfully installed them but cannot run all the OpenNI examples or any of the Astra SDK examples, though that may be a separate issue.
I am of the opinion that the "develop" page on the Orbbec site exhibits UX deserving of improvement. As a new user it's not clear that the "hardware and software you’ll need to get started", including the driver itself, is in fact only available in the provided OpenNI download package. The OpenNI/Drivers download is under a section labelled only with the OpenNI logo. The section itself adjacent to but does not precede the actual SDK download section. With all this under consideration it is difficult for me to say how one would intuitively understand both the requirements and order of steps to successfully complete the installation process. I believe minor adjustments would prevent any reasonable confusion from an individual in my situation.