PX Policies are unable to get/set account attributes using the functions under the Accounts Category within the PX Policy if the account we are trying to operate against is not correlated to the IM/Provisioning user that is the subject of the task.
All Identity Manager
The PX Policy Data Elements and Action elements found under the Accounts Category are designed to only work against accounts that are associated to the IM/Provisioning user that is the subject of the task. You cannot set or get account data using these PX Policy functions for any account you want.
You will need to do is look at using a Data Element of LDAP Query found under the Data Sources category instead to retrieve desired information.