This module manages roles via the organizationalRole object class. There is also a user module to manage memberships on the user edit page.
Activate the account type "Groups" in your LAM server profile to use this account module. Alternatively, you can use the account type "Group of names".
Then add the module "Role (organizationalRole)".
On the module settings tab you set some options like the display format for members and if description should not be displayed.
You can add any accounts as members. This includes other roles which leads to nested roles (needs to be supported by LDAP client applications).
To show members of nested roles click on "Show effective members". Please note that for large roles this will run lots of queries against your LDAP server.