I think this is allowed multiple activation, as we have done migration twice in past years.
Also on their portal following is listed..
....
SmarterTools products may need to be reactivated if they are moved to another server, upgraded from a previous version, or assigned to a different database. As a fraud protection measure, Smartertools customers are allowed two reactivations per product by default. In addition, the same license key may be activated on two servers within a 30-day period without triggering SmarterTools' fraud protection alerts.