Is the repentance of one who hacked Facebook accounts to obtain shipping codes for purchasing applications, then donated the value of what he stole due to the impossibility of returning it to its unknown owners, acceptable?

You have done well in repenting to Allah, and that is a favor from Him. Among the conditions of repentance from violating people's rights is to absolve oneself of them by seeking forgiveness or returning the right to them, even through indirect means, due to the hadith: "On the hand is what it took until it fulfills it." Giving charity on their behalf is not sufficient if it is possible to deliver it to them, and there is no need to inform them of the deception that occurred. If it is impossible to deliver his right to him and you despair of doing so, then give charity on his behalf.