I used a soundpack addon for old OFP. Will it work in OFP: Resistance?

It will most probably not work, if you try installing it in OFP: Resistance's separate folders. Besides, OFP: Resistance introduces its own new and improved sounds to the game.

Your old soundpack will continue to work with the old version of OFP. Remember, OFP: Resistance hardly modifies your old OFP version's folders or files.