Can I sacrifice a unit with the [whi]Grudge Thrower[/whi] ability to let [whi]Dwarf Ranger[/whi] do a damage outside of the combat phase?
If the answer is yes, will the attacking/defending units receive the bonus when, after the sacrifice, combat phase starts?

Nevermind, got my answer from the James' Rulings. the answer is "yes" to both questions.
Anyway another question comes to my mind: can I use the [whi]Grudge Thrower[/whi] action [u]after[/u] the combat phase?

hmmmmmmm

which are james rulings?

thats interesting
i would hav thought, that you werent able to sacrifice unless a combat is about to happen!?

or is it like your own responability if u would even throw away the effect of the sacrifice in case no combat would happen this turn?

From the Warhammer Q&A Thread in this forum:

Q. If I play a card like Waaagh! or use an action like Grudge Thrower before combat, do I get the bonus?
A. Yes, that kind of action creates a continuous effect that waits for the appropriate time to give the bonus.

well, then its another last-minute-damage :)