If the search head is able to connect to all of them, then yes you can setup database connections to all of them: http://docs.splunk.com/Documentation/DBX/latest/DeployDBX/Createandmanagedatabaseconnections
Then just dbxquery connection=connection1 ... | append [dbxquery connection=connection2 ...] | ...
If not, you could also setup DBConnect on a Heavy Forwarder in each region, have these HFs regularly query and index data and forward to your Splunk indexer(s). Then just use normal Splunk queries to search the data. This has the downside of using Splunk Enterprise License (as you are now indexing data into Splunk), but a potential upside of adding indirection between your search head users and your database. (Obviously, you'd need the network paths open to either forward data, or search across remote Splunk indexers instead of the database connections).
If the search head is able to connect to all of them, then yes you can setup database connections to all of them: http://docs.splunk.com/Documentation/DBX/latest/DeployDBX/Createandmanagedatabaseconnections
Then just dbxquery connection=connection1 ... | append [dbxquery connection=connection2 ...] | ...
If not, you could also setup DBConnect on a Heavy Forwarder in each region, have these HFs regularly query and index data and forward to your Splunk indexer(s). Then just use normal Splunk queries to search the data. This has the downside of using Splunk Enterprise License (as you are now indexing data into Splunk), but a potential upside of adding indirection between your search head users and your database. (Obviously, you'd need the network paths open to either forward data, or search across remote Splunk indexers instead of the database connections).
Nice! Wasn't aware that was possible. Thanks.