If I have a regular Ninetales in my hand and an Alolan Vulpix on my bench, can I evolve the Alolan Vulpix into the regular Ninetales?
Alolan and non-Alolan forms are not interchangeable because they have different "names"
The 2017 Pokemon Trading Card Game Rules in the section What does and doesn't count for a Pokémon's name? makes it clear that the Alolan and non-Alolan versions are not the same Pokémon.
An owner or form name in a Pokémon’s name is part of the Pokémon’s name:
- Meowth, Alolan Meowth, and Rocket’s Meowth have different names
There are other rules for what counts as the same or a different name, but for our purposes, "Alolan X" is not the same name as "X".
The "evolves from" name must exactly match the name of the pre-evolutionary Pokémon
From the same section:
When evolving, the “evolves from” Pokémon name must match the Pokémon being evolved. So Graveler can evolve from Geodude, or Geodude LV. 12, but not Brock’s Geodude.
The "evolves from" Pokémon is referring to the Pokémon in the upper left corner of an evolutionary Pokémon.
Alolan Pokémon follow these same rules
Consider Alolan Persian:
Alolan Persian's card says in the upper left corner "Evolves from Alolan Meowth". Since "Meowth" is treated as a different name, you cannot evolve a Meowth into an Alolan Persian. This is reiterated in Appendix K of the rules:
Note that “Alolan” is part of the Pokémon’s name—this means that Alolan Persian can only evolve from Alolan Meowth, not from Meowth. Also, you can have up to 4 Persian and up to 4 Alolan Persian in your deck if you wish.
There are some circumstances where a non-Alolan Pokémon can evolve into an Alolan Pokémon, such as Alolan Raichu.
In this case, the upper left corner of the card explicitly says "Evolves from Pikachu", thus a regular Pikachu will work (but not something like Surfing Pikachu, as fitting as that might be).
In your particular case, Ninetales' card says that it evolves from "Vulpix". Since "Alolan Vulpix" is considered to be a different name, it cannot evolve into Ninetales. Similarly, an Alolan Ninetales' card would say that it evolves from "Alolan Vulpix", so "Vulpix" cannot evolve into it.