Just because I didn't see it explicitly stated... yes, any audio from SONAR or your file system can be dropped into the sample window for one of the DR layers. That window can also be clicked to open a file open dialog that will let you pick your own files. I think FLAC, WAV, OGG, MP3, etc. should all work.
Addictive Drums uses a proprietary sample format (I think), so content cannot be dropped in from the synth directly. However one of Bill's methods (or just freezing a DR track with one note for the hit you want) will work.