I've recently learned the following about the Japanese dubs:
Star Wars and Empire were both shown theatrically dubbed; Jedi was shown theatrically exclusively with subtitles. Later, entirely new dubs were made for all three films, using famous Japanese voice actors, and these dubs were used for home video releases. These video dubs have become the most familiar/popular versions of the Japanese dubs. The Japanese GOUT discs featured both dubs.
As for the dubs themselves, the only unusual bit I've found is that Greedo is dubbed over in Japanese (Jabba is not). In the video dub, a little electronic distortion is added to his voice, probably to make it sound more alien.