But all the reports & dashboards are created with weblogic user only.
So are you saying that "Only the user weblogic is ever used to create reports and dashbaords"? Because if you use that user to create content then of course it's visible to him...
For the rest: Yes your request is doable but I'd be careful because if you lock out weblogic (or any other admin-type user/application role) then you may run into issues where your content becomes inaccessible.
Yes, we use weblogic user to create reports & dashboards and use the same user for migrations. If that is the case is it possible for us to create another user with admin access similar to weblogic and use that user to create those specific reports & dashboards..
Yes, of course it is, because it's a bit weird to use "weblogic" for creation and the expect things to be "hidden" from him.
It would be good if you understood how security works though before attempting to revamp it: http://www.slideshare.net/GianniCeresa/obiee-security-its-a-jungle-out-there