Oracle has released a Metalink Note on the proper procedure for setting passwords for the database and FNDFS listeners. It is important to note that there are two listeners in an Oracle Applications 11i implementation. The first is the standard database listener and is the version from the installed database. The second is for FNDFS/FNDMS and is used by the concurrent managers, generic service manager, and other internal Oracle Applications processes. This second listener is part of the 8.0.6, thus is version 8.0.6.x. Passwords should be set for both listeners, especially the 8.0.6 listener since it is such an old version.
A recent AutoConfig configuration templates patchset (August 2006 - TXK.N or later) and Rapid Install (ADX.F + post fixes) are required in order to set a listener password. The Metalink Note states AutoConfig Rollup Patch N or higher, so at this time Rollup Patch Q August 2007 (5985992) is strongly recommended.
Follow the instructions in "How to enable/disable/change password of the listeners for Oracle Applications 11i" Metalink Note ID 386374.1 (Metalink access required).