it depends the game itself.
If the developers added options, or missions, or anything which changed the way the savegame data layout is stored, then it will make it incompatible because it will be incorrect size, with data at incorrect location in the savegame.
for info, xenobladeX savegame works on other region console.
You also didn't mention if the "X region save" is the one from a game or from a console.
As the WiiU can play game from another region, then there's no issue having a "X region game save on Y region console".