Okay, now I could login with other users also. I'll tell you what did I do -
Go to Users and Groups > Administrative User Roles
Here, I added those users with appropriate roles (administrator or operator or whatever), these users has to be present in LDAP repository (else you can’t add them here).
Now I am able to login with other users also (which I’ve just added)…
This is fine but what I wanted was that I don’t use websphere admin console to add users – guess there should be some way to do all this in LDAP repository itself…