The gentoo nvidia-drivers ebuild does not install nvidia-settings, nvidia-xconfig, libnvidia-cfg.so* or libnvidia-wfb.so*. There is a separate ebuild for nvidia-settings, but not one for nvidia-xconfig at present.
To use nvidia-xconfig just unpack the driver (sh *pkg.run) and you will find it, along with libnvidia-cfg*.so so you can use -a. (Then, make an ebuild for nvidia-xconfig based on nvidia-settings, put it in /usr/local/portage overlay, test and then when done attach it to a bug report. Instant developer
The difference between pkg0 and pkg1 is that pkg1 has a lot of precompiled modules for different distros, and is about twice the size. The gentoo nvidia-drivers ebuild compiles from the source provided.