The problem with that is you are needing the business rule to run off the sys_user_grmember table and setting a value in the sys_user table.
Plus, we've determined that it runs when you manually add/remove someone from the group, so the business rule seems to work.
Here is what i would do.
Create a new community post with the question of why is my business rule not running on the LDAP import explaining that it works when you manually add someone to the group, but when the transform map does it, the business rule does not run even when 'run business rules' is checked.
This might find someone who has an answer to respond since this issue is not obvious from the current post question...
