With not having experienced this first hand, what I would do is run a sql query against the taddm database, pull out the hostname and ips (and server groups if they exist); put it in the csv format that you can import into CCA from the web ui.
Once that is done, manage those servers and its data from CCA; run the initial discoveries and get the data you need \ want. I personally would not try to get the data over from taddm; i rather use our data \ datastructure \ technology to get the data