What I do for a particular campaign is add the following to the flow:
Unsubscribe = False
Add to list = (the campaign suppression list)
and because we have an opt out type pick list in SFDC, I do, Do not email type = {lead.Do not email type}the campaign suppression list
The above option allows us to send our customers their paid subscription emails which they are expecting and which we can't really make operational. When they get promotional emails, their unsubscribe status will not keep them unsubscribed from receiving their paid subscriptions. They are instead added to a suppression list by campaign type.