If I use any of the AppleLoops supplied with Logic 9 in my project, will I be subject to an liability or royalty? If yes, how can I reach those persons who lent their voices to the loops?
All of the AppleLoops supplied with Logic or purchased via JamPacks are licensed to you for unlimited, perpetual use in any derivative creative work. That is: you can use the inside of your own music, but you can't just give away or resell the samples themselves.
For example: if you made a "song" that was one AppleLoop, looping for 3 minutes, and tried to sell that. Well, that's not really a derivative work because it's just the loop and nothing else. You couldn't give that away or sell it. But combine two of them together? Now it's derivative (it is unlike either of it's pieces, a new thing unto itself) and you can give that away or sell it as you, the creator, see fit.
Enjoy those loops! Make lots of awesome music!