We have a custom object Employee. Created a lookup field with Employee object (Self - lookup) called as Manager. Whenever submit to approval Manager should be approve. But manager unable to approve because its not a user. Ex:- we have a 2 records like developer and Team Lead. Team Lead Should be approve of Developer.
Here is some documentation on approvals in salesforce https://help.salesforce.com/HTViewHelpDoc?id=approvals_creating_approval_processes.htm . Note that approvers must be Salesforce users to your org. Only on the user object can you set a special user Hierarchical Relationship field type. You can add more fields of this type on the user object to meet your needs, but all the users must be active salesforce users.