In VR, regional variants will give birth to regional variants, regardless of where they are bred. So a Hisuian Growlithe would always produce Hisuian Growlithe eggs, an Alolan Vulpix always produces Alolan Vulpix offspring etc.

Breeding a Hisuian Growlithe to a regular Growlithe would produce a mix of both Hisuian and Kantonian offspring, with the distribution being similar to breeding two different species of pokemon -- there'd be a 75% chance of each individual offspring being the mother's regional variant.

The only exception is if the regional pokemon has a universal base form. As in, Both a regular Raichu and an Alolan Raichu will produce Pichu eggs.