Hello,
The adm-PassswordSelfServiceEnrollmentPolicyDN attribute mentioned in that post is still available and supported, however you cannot use it for building Business Units. The thing is that Adaxes virtual attributes (all attributes with the adm- prefix) cannot participate in LDAP queries. Including Adaxes virtual attributes in LDAP searches would have a tremendous adverse effect on the overall performance.
As a workaround, we can suggest a Scheduled Task that would run a several times a day and copy the Password-Self Service Policy DN into a certain actual AD attribute that can participate in LDAP searches and that you don't use. For example, you can use such an attribute as Division. Then, you can use the attribute for building your Business Unit.
For example, here's a Scheduled Task that copies the Policy DN to the Division attribute:
In this case, a Membership Rule for a Business Unit containing all users enrolled for Password Self-Service will be as follows: