John,
Are you looking to manually add nodes then have their custom properties fields populated by data from your cmdb? If so then I use SQL Server linked servers to pull data by SQL job, trigger, or powershell script. If your cmdb is also SQL server-based and you can get the DBA's to work with you to link this is an easy approach.
If your CMDB is not SQL server based and/or you mean you want to import the nodes from data provided by the CMDB then you should download and start learning the Solarwinds SDK. I am currently writing scripts to import nodes and have found only small caveats, like adding asset inventory to nodes, and its provides us a pathway to import and select exactly the objects to monitor based on a template vs hoping everyone remembers the training.
Hope that helps guide you.