I have seen some of
Marc Adamus' work. He uses ND filters (not split), to allow extended shutter times, and fair depth of field. He uses this technique to eliminate details in moving water. Very interesting work.
I did use split-ND filters when I shot film, and occasionally with digital. Film gives you one frame to do the job, and that frame can not be manipulated easily without darkroom equip. My lanscape film work was always with slide film. If the light was not within the latitude of the film, I was forced to use a Split ND filter.
With digital, I can shoot to the middle of the exposure range (in RAW) and create the image I wanted, in the computer. Worst case, I can use multiple shots and use HDR techniques.
If the image will be a sunset or moon (something moving or changing fast), I am still forced to use a Split ND filter on occasion (if the light is too dynamic).