Hmmm, I've tried that before and what I end up with is:

Is there some hidden step to adding Dealer as a Child Row Group that will move it underneath the Division Row Group that I'm overlooking, or am I just being dense about what I can do with the formatting?

The only way I can get the Dealer Row Group under the Division Row Group is to add it as a Row Group Adjacent Below, but that obviously just outputs all the Divisions first and then all of the Dealers underneath that.