The default driver is "nv", but that's a different thing altogether. That's an XFree86 driver, not a kernel module. NVdriver (and the new name for it, nvidia.o) are kernel modules; nv_drv.o and nvidia_drv.o (the first one should be under /usr/X11R6/lib/modules/drivers, and the second will be put there by the NVIDIA_GLX package) are X drivers.
Yes, recent modutils allow modules to be gzipped on disk. They do decompress them before loading them into the kernel.