Well… after some investigation I am concluding that there is no way to retrieve a User’s defined groups or rooms from the API. The discussion thread here confirms this:
Wish I had better news. So instead I am now working on making the initial rooms fully editable, including deleting some and adding others. I will also likely modify the default rooms to something more generic. At present I use a regular expression to put certain things into certain rooms by default which I think makes sense. I will probably stay with that but ditch some of the default rooms like Thermostats which I think is not likely to be a commonly desired group.