I think I have heard of it, but not sure what direction, i.e. which was the rootstock.
Also Black Sapote is evergreen, but Kaki and American are deciduous.
However that is not an issue in Citrus ( deciduous Trifoliata rootstock under evergreen Citrus varieties, and the reverse combo is ok )
I think Kaki is compatible with some other Diospyros as rootstock. ( Date Plum and American )
Diospyros is also a very big Genus, and not all are closely related.
Some Australian Diospyros species seem close to Kaki in fruit and foliage, some quite different, some like mini Black Sapote.