The V17.5 hood has 67mm threads, and it looks plenty sturdy enough to allow attaching a filter out there. I would guess most hoods are designed to allow the maximum possible shading of the front element without any vignetting. So I'm not sure but I would expect some vignetting putting any kind of filter on the hood. Using a regular or thin non-variable ND between the lens and the hood might work better and be less expensive.
If it's like the 25mm hood, it does have filter threads. Though in the instructions it does say specifically not to do that, as it will vignette. I think the vignette would be worse on a wider lens if you put a filter on it.