Does OEM keep track of all the tasks performed on it by user. Suppose a user say "A" has created a group or incident rule and a user "B" deleted the group or incident rule created by user "A". Now can the sysman user or "A" user would anyway know the fact that the user "B" has actually deleted them. So does OEM keeps the tasks performed by its users somewhere where it can be checked and confirmed?
Yes, EM has it's own auditing, although it is set up at a minimal level to begin with including EM login/logout. You would want to enable additional auditing to monitor this type of activity. See the Security Guide for more information: