And perhaps it wasn't the Empire that was hated at all, but Palpatine. A bunch of people hate George W. Bush without hating America; people hated Hitler without hating Germany, and people hated Hussein
without hating the nation of Iraq.
It's possible that these people were only celebrating Palpatine's death and were still loyal to the Empire. It's also pretty clear in the EU that many Moffs and officers hated Palpatine. The Empire under Thrawn was much more efficent because Thrawn wasn't evil per-se, but just really cold... and the similar goes for Pealeon.