As far as I know "undub" versions of games are the same regional release with different voice-acting sound files. Like, Arc Rise Fantasia, a Wii game with an undub version, is just the NTSC-US with the mentioned sound files changed. It will use the save files of the NTSC-US version only.
This is because games have regional IDs, so a Japanese save file would not be recognized by an American release of the same game, at least, most of the times, because the IDs would not mach. Technically they'd be seen as different games; but even then, many times there are incompatibilities if you try to force a non-japanese save to a japanese game or viceversa.