The only sure fire way to see what the app isn't using is to setup logging and run through a full exercise of the application. This can be done from the client and/or server.
You can log the JDBC activity with log4jdbc or You can also have the DBA setup a trace on that spid.
And a good DBA aught to have a job scheduled in production to gather periodic snapshots to see what's happening, this may help you depending on whats being monitored.
After you've identified candidates for removal, you can create an ObjectLog Table and script out triggers on the tables and call in each proc to insert into that table. Running that in production for a while will give you the confidence to drop away.