Does a non-Alolan Pikachu evolve into an Alolan Raichu or a normal Raichu?
Transferring an older generation Pikachu and evolving it in US/UM will result in an Alolan Raichu, not a non-Alolan variant. To obtain the non-Alolan variant, you have to evolve it whilst in Ultra Space. Being from an older generation does not make a difference. This also means that there is no way to evolve a Pikachu in Sun/Moon into non-Alolan Pikachu without trading it to US/UM, since Sun/Moon doesn't have Ultra Space.
This also applies to Exeggcute and Cubone.