Answer
This depends on the release — later Apps10 updates added a PL/SQL Routing Address destination type that lets a Routing Address call a PL/SQL method directly, without going through a BizAPI. Older releases, including IFS9, don't expose that option in the Destination Type dropdown when creating a Routing Address, and there's no configuration-level workaround to get it there. On IFS9, the available path for the same kind of scenario is to invoke a BizAPI asynchronously (for example using plsqlap_server_api.Post_Outbound_BizAPI), with the BizAPI itself deployed on the IFS Application server, rather than routing directly to a bare PL/SQL function.