For example, say I have a drum loop that’s sliced up all on one track. Can I pan each hit/part manually? Or is automation and/or offline processing each part the only way to do this? Maybe I’m missing something completely obvious here. 
Yeah, that’s it, offline processing on the parts or automation as you say. There’s no way to pan a part. I’d probably go for automation I think, and then make sure automation follows the parts (preferences).
Well, actually another way perhaps is to get into GrooveAgent because I believe you could probably drag all the parts into GA and they’ll line up on the pads, and you can also do some midi magic to make it play. Then you could pan the pads in GA. I’m not an expert but there are plenty of vid tuts on how this works.
Mike.