Yes, you do. Since there are loads of spare units (Tyrande, Furion, etc). Get WinMPQ to find out the filenames and directory's of the units in WC3's MPQ, and name them so in a Campaign file.
Yes. Just load the MPQ's with WinMPQ and it will list all the files. Change the filter to .wav for just the wav's. Find the unit you want and name your wav's like theirs in the Campaign file.