We intend to use Mandrill for all our transactional emails but in this specific case we have reminders that we send periodically if a few user requests are not acted upon for too long.
The idea is for us to give the users the option to stop these if they choose to.
We initially thought we could handle unsubs ourselves but since Mailchimp requires the UNSUB tag I imagined something similar would be required from Mandrill. But then again as you said, unsubscribe links make little sense for welcome and password reset type emails.
If Mandrill is more flexible with this then we can start simple with mailto:
un...@domain.com links until we have our user notification control panel up and running.
Whatever the policy is we're good.