Dinesh,
How did you get on adding new roles? I am trying to do the same thing at the moment and have added a new role in http://IP/admin/rel-types/roles/ and also added a new relation type at http://IP/admin/rel-types/ which is a subtype of dotLRN Profile User.
This new user type does not appear on the drop down list when I try to modify existing accounts or add new ones.
Thanks,
Matthew