Hello,
I'll try my best to answer your question,
1. If they are clustered, you can determine which App is connecting to which DB.
2. If we are talking about a standalone LPAR (no cluster), then DBA is your best shot (considering oracle is the DB), one can look at tns.ora file to see what application(s) are connecting to DB(S).
3. Assuming you are a System Admin and your team maintain and inventory sheet of all servers.
But just by seeing the output of netstat or ifconfig, one cannot determine what connects to what.