Who better to form a Rebellion than those who were part of the Imperial machine? Most important characters in the Rebellion were part of the Empire, or tried to be, particularly among their pilots.
Luke pined for the Imperial Academy, while Uncle Owen kept him on the moisture farm.
Han Solo was an Imp officer.
Princess Leia Organa was an Imperial Senator.
Biggs Darklighter was an Imp officer.
Tycho Celchu was an Imp fighter pilot.
Baron Soontir Fel was an Imp officer and fighter pilot. (How many Rebels did he kill before joining up with the New Republic?)
Hobbie Klivian was an Imp officer.
Jan Dodonna was an Imp officer (former Republic officer).
Mon Mothma was an Imperial senator
Princess Leia Organa was an Imperial Senator.
Garik Loran was a child actor for the Empire!
I'm sure there are more. This seems like a fertile background for characters. Most of the characters above appeared in the original trilogy or the X-Wing novels.
This would be a great Rebel campaign, starting as Imps, seeing the nature of the Empire, but deciding to stay in and try to work as sleepers. It is what the early Rebels did, according to Zahn, and later, Lucas.
Edited by Jedi Master Gunner