Dear Dear R@Dhe,
There are two categories of employees. One is those who are workmen under the ID Act and another is non-workmen, i.e. Supervisors and Managers.
The settlement or agreement between the employer and workmen, whether it is arrived at in the course of conciliation proceedings or not, and an arbitration award, all are per the provisions under the ID Act.
Whereas you can not arrive any settlement or agreement with Supervisors and Managers or have arbitration award under the ID Act since the Act is not applicable to them.
However, you can have separate agreement with such non-workmen category which will not be as per the provisions under section 18 or 2(P) of ID Act.
Hope your doubt is cleared.