Hey Rose,
To be honest, the best way to make sure you didn't burn the bridge when you left without notice is to make contact with your prior employer and see if he will recommend you favorably if they happen to call him (probably not). If he balks, I guess you could still list it, since it IS your experience and you'll have to account for the empty space somehow anyway, but smoothing things over w/ the boss man is a good idea regardless.
I can't see how him being a preceptor will matter a hill of beans to the AdCom. If nothing else, it might actually HELP your chances. The pharmacist I volunteer under at the hospital graduated from my school of choice, and she suggested that it would be a very good thing.
YMMV, HTH.