What is the impact of changing the IP Address of any DB server if used for any of: Task Persistence, SiteMinder Policy Store, SiteMinder Audit DB, IDM Audit DB, and IDM Workflow?
The impact of changing the IP of the DB depends on how the connection to the DB was specified. Basically if the IP of the DB machine will be changed, but the machine name is not (assuming your DNS is functioning correctly) and all the connections to the DB were configured such as the machine name, etc... then everything should function as normal and there would be no impact to your Identity Manager solution.
However, if the entire connection configuration to the DB was set as the IP Address of the machine, then your Identity Manager system will not be able to function. In this case, you would have to go to the connection configuration, one by one, and set the new IP address.