I found the API documentation in the PLDS downloads for SBCE (not in DevConnect where it probably belongs).
The current implement of the APIs is missing many config items (such as adding/remove URI Group entries), in addition to not being enabled by default and not using the REST model.
Hopefully future versions of SBCE will include further configuration items, and possibly make available the statistical and registration data, and be easier to consume via the standard REST model. This would allow SBCE management to be integrated into other tools in the same way SMGR can.