I'm not sure about an AD service, but you can use the User Profile Service (GetProfileByName method) to retrieve the manager username for a user(s), and then you can use the same service (Manager method) to retrieve the Manager's email address. To do this, you have to be able to submit the user's name and the manager's name to the web service as a directed query, and then it returns the data. I am not sure if this will work when sending the results of a double eval, but it does work when sending individual names.