On the rare occasion when I use a 24mm f/2 Nikon lens for a landscape on my 35mm film camera, I may use a Cokin-type graduated neutral density filter (see middle filter in attached image).
I have 24mm in Minolta A mount and M42 and a 25 mm in Miranda mount, never needed a ND graduated filter to correct for dark corners but then again my lens are 2.8.
We are seemingly talking about two different kinds of filters:
-) neutral, linear graduated (arbitrarily graduated, for image effect)
-) neutral, radial graduated (graduated for a specific lens, against its vignetting)
With vignetting of wide angle lenses one has to differenciate between optical design:
wide angle lenses for SLRs are of the retrofucus type and concerning their outcome cone they behave as lenses of longer focal lenght and show much lesser natural (cos4) vignetting than plain wide angle lenses.
But there are other forms of lens vignetting too, thus one must look at each design..