Yes you can call a Siebel BS from Java.
Several ways to do this. See the bookshelf for details.
Lead Architect and Director
Ponder Pro Serve
The Bus Comp that Business Services are listed under is 'Repository Business Service'
Using Java you can create (or connect) to a Siebel instance and execute a query to pull back all of the Business Services based on that Bus Comp.
Look in Siebel Tools Help under : Siebel Object Interfaces Reference > Interfaces Reference > Application Methods > Attach Method for a code example of using Java to connect to Siebel.
Information about which methods are usable in Java (for the Java Data Bean interface) is located in Tools help at:
Siebel Object Interfaces Reference > Java Data Bean Quick Reference >