For moves that existed in the data of the original games, but were only added to moveset compatibility in USUM (such as Strength Sap on Vileplume or Meteor Mash on Lucario), those can certainly be transferred back.
The new games also introduced three new moves into the game data in the first place: Mind Blown, Plasma Fists, and Photon Geyser (plus a few new exclusive Z-moves that rely on items like Kommonium Z that didn't exist before at all). If you put any of those moves on a Smeargle, you will not be able to trade it to a player on the original games.
