Why Saboteur is a bad choice even with Palpatine around:
1. You need to decide to use Palpatine on Saboteur before you know if Palpatine would be better used during Combat.
2. Crew slots are valuable. There's almost always something more useful to put in them.
3. You need to burn an action to activate it.
4. Even with Palpatine, using Saboteur is still a gamble because some crits just aren't worth it.
It boils down to the same problem as Expose: in comparison to the benefit you get, you're paying too much of too many different kinds of costs.
That's not to say there isn't a consistently winning squad out there that features Saboteur (or Expose, for that matter). And if for some reason your life's goal is to optimize Saboteur, the Emperor is an effective way to do it even if it's not efficient.
But if the question is how I would build Palpatine + Saboteur, the answer is that I wouldn't.