While it is technically EU, I remember reading in some books and on the back of action figure cards that Wookies were used as slaves during the age of the Empire.

While we don't see them get enslaved in ROTS, I noticed that the inhabitants of Utapau were being taken into custody by the Clone Troopers after they had beaten the droids. Seeing as how Kashyyk and other systems were invaded and then aided by the clones, is it possible that Sidious decided whichever planets they "saved" were enslaved after they executed Order 66? While a ratty thing to do, it does make sense since the manpower to do it was present and all.

Well, the droids did invade Naboo, but I don't think Palpy would have enslaved his own home planet (in TPM, he was Naboo's Senator). Maybe the woookies were just too primitive of a bunch to have any political voice even in that so-called galactic senate.

Yes, but Naboo was invaded pre-clone wars. I am referring to the systems invaded during the actual war.

Actually it did show in ROTS that they were taking control of the Wookie planet. Remember those Stormtroopers on those walker things after they turnnd on the Jedi? They were looking around and mentioned all the wookies around were dead and to move on.

I thought maybe those wookies were dead from droid attacks.