Reality does not show in the DAZ Installer Manager
That is correct. Reality includes a plugin but it is a stand-alone program and the DIM is not usable for the installation of the program. There are several installation operations that need to be custom-tailored for Reality.
Reality is distributed as a zipfile. Uncompress the zipfile and in there you will find an installation guide in PDF. Read that guide, it has all the details that you need in order to install Reality. In general it's just a matter of running the RealityInstaller program.