It depends on what auditing tool you are using as to what information you will see when you read the log information. You can see the values of any variables passed in a select statement, but then I am using Iderra's tools (Compliance Manager) which is more robust. The only time this becomes an issue is when the developers write an application where all the connections to the database are made with some bogus login user. You can buy managment tools for that as well to see who is connecting (ports, IP & MAC addresses and LdAP usernames), but you are talking a lot of money for that much control. This also means performance managment also.
You can try using RedGate's SQL Restore to view the audit log and it will tell you the absolute values. This is a free tool last time I checked.