It's a drop-in replacement for the nvidia package. AFAIK there are zero differences in functionality. The only change is it being built locally by DKMS instead of coming pre-built.

It builds the kernel module for your specific kernel. It's not different from the nvidia package, that's just the same thing pre-build for the default kernel (in fact if you install both nvidia-dkms will build the module locally, then realize the exact same thing it just build is already there and move on...).