Comment 34 for bug 526892

I was able to fix this with the following:

 * In /etc/modprobe.d/blacklist-framebuffer.conf, comment out "blacklist vesafb" and add "blacklist vga16fb"
 * In /etc/initramfs-tools/modules, add fbcon and vesafb
 * Run initramfs-update -u

With that, I get a working Plymouth with the proprietary Nvidia drivers installed. I also added the 'vga=' line to the kernel commandline in grub, not sure that's necessary or not though.