Yes, in XF86Config, you have to be using Driver "nvidia". You also can't say Load "NVdriver" up in the Modules section.
You're getting errors from X that it can't find NVdriver, not from your kernel. Which means that you told X, somehow (almost always, through the config file), to load a module called NVdriver. There is no such thing -- X looks for its modules in /usr/X11R6/lib/modules/extensions (and /usr/X11R6/lib/modules/drivers for Driver "xxxx" lines), for a file named lib<module name>.so and lib<module name>.a. So if you have a Load "NVdriver" line in there, it's looking for a libNVdriver.so and libNVdriver.a file in the extensions directory. Obviously, neither of these exist.
You need to be telling your kernel to load the NVdriver kernel module, not X. A lot of distros do this with /etc/modules (they alias either char-major-195 or /dev/nvidia* to NVdriver in that file), but some (like Slackware for one) use an /etc/rc.modules file that just lists all the modules to load. If Gentoo works that way, then just add NVdriver to the bottom of that file.
If you're saying Driver "NVdriver", then change that to Driver "nvidia" (so it looks for nvidia_drv.o rather than NVdriver_drv.o in the .../lib/modules/drivers directory), and if you have a Load "NVdriver", get rid of it.