I think we've seen normal Vulpix roaming around Kitakami already, so I doubt Alola Vulpix will be there too. Wouldn't surprise me if we can just get one in game, though.
Also not sure on the number of regional variants of base game Pokemon we'll see out & about in general. Like, I keep looking back to Normal Wooper, who got its dex scrubbing. I think that happened because while it was available in the base game, it did not have an entry. So if we follow off of that, if we wanted Hisuian Growlithes to run around, we'd probably see Growlithe & Arcanine get scrubbed entries because Growlithe-H didn't have a dex entry to begin with.
Conversely, normal Tauros could be in either DLC: Normal Tauros already had a dex entry.
And continuing this it's not to say that the beach zone wont be Alola-flavored and allow Pikachu to turn into Alolan Raichu, just that Raichu-A isn't getting a dex entry.