Does UnderStock Matter with certain cultivars.

I asked the grower where I got my Pictum (usugumo).

In all my readings, it seems it's generallt Acer mono that is used for the understock for this ?

Anyhow, grower just replied and he said it's just regular palmatum.

As long as the graft took *scion* grew and tree is growing, how much or how little will the understock change the cultivar of the plant's characteristics ?