I know this Thread is way old, but I figured I'd drag it back up to answer the question in the last post. A Sith Lord discovered the Rattataki, enslaved them, and trained them as acolytes. He saw their amazing battle skills and exploited them. Something happened to him like it happens to all Sith lords and most were killed. But by this time, there were a lot of them as slaves to the Empire, and some even received full training. At least, that's what a Wiki told me