Grafting does 2 things:

1 - The rootstock gives growing characteristics, such as disease resistance, size, hardiness, suckering, etc.

2 - THe scion gives the fruit characteristics, such as taste, size, etc.

It may be variation of the seedlings, but you could have also lost a few (it happens). You sure the buds are alive on the "dormant" ones? If youre worried about late frost, id graft on the later leafing rootstock, to help delay flowering time (another reason people choose certain rootstock).

As far as I know, you only worry abou tfruit type in regards to scion, the root stock does the rest.

The phenomenon that you are witnessing is very real and can be an important determinant in the cold hardiness of grafted Asian persimmon trees. I have reada couple of anecdotal accounts of this and see it in my orchard on a yearly basis - some American persimmon trees break dormancy several weeks later than others and do this consistently from year to year. I have a tree from EL that consistently shows some frost damage on the leaves after budbreak during a normal year; this year the tree leafed out earlier than the others and is now toast after a 25F exposure. Most of the other trees I grafted myself onto rootstock that I know to be late in breaking dormancy and none of these show any foliage damage. The latest breaking American persimmons have in my experience been from the Morris Burton lineage and these are just now showing the earliest signs of breaking bud.

I have several Asian persimmons and one American and a couple hybrids. Just like how the varieties have different characteristics such as early bud break, so would be seedlings grown trees.
Bud break is influenced by the warm weather causing the sap to flow, the rootstock have a direct impact on sap flowing causing the buds to wake up. So I'm sure rootstocks that leaf early can cause the scions to grow earlier.

So far, the two persimmons that are still dormant for me are Hokkaido and Nikita gift. Regardless of the rootsock these two are known to break dormancy late.

Bass