Hi Tiago; long time no see :-),
Starting with the easiest answer, the component can work with multiple AD instances, though I haven't tested myself. If you're making different operations in the same flow you might have to call the set domain action multiple times to establish new connections as required.
Not using the Users tenant from OutSystems makes it harder to manage sessions and logins, but it is possible. The component does not have any connection to Users and it even has a method to validate the login directly on the AD.
Cheers.