Hello Frank,
Ideally there is a Discovery Profile scheduled to run on a regular basis that contains IPs for managed devices. That is the best way to keep things up to date, alongside the automatic Change Detection updates the Metric Families in the Monitoring Profiles go through.
REST can also be used to create, update and launch Discovery Profiles.
This section of the documentation appears to provide instruction for the very task you're looking to accomplish.
Automate Device Inventory Synchronization - CA Performance Management - 3.5 - CA Technologies Documentation
If you want to look directly at the REST pages a good place to start would be these URLs.
(replace DA_HostName with your DAs host name or IP address)
http://DA_HostName:8581/rest
Which leads to three different REST documentation pages for Discovery functions.
http://DA_HostName:8581/rest/discoverydefaultconfig/documentation
http://DA_HostName:8581/rest/discoveryinstances/documentation
http://DA_HostName:8581/rest/discoveryprofiles/documentation
Hope that helps!
Thanks,
Michael