Am I right to assume that while a Hero is "sacked" (Carrock treachery) I still can use his resources that remained in his resource pool and that I even can assign damage to him (like undefended attacks)?

You are indeed correct. Sacked! gives you a list of things that you may not do with your hero, and the two things you mentioned are not on that list.

So, thematically the sacked hero is like a vegetable that I can rob and beat up?

Bonus Card said:

Yes, and if you're a troll you can roast him for dinner.

Kiwina said:

Nonsense, everyone knows that trolls don't eat vegetables