Yes, the Smart Campaign would be a recurring campaign, set to a daily schedule. However, the qualification rule would reflect the number of days (e.g. 30 days) of inactivity you are looking for in your Smart List. This way, if you are looking for inactivity of 30 days, the campaign cannot run on the individuial lead for another 30 days.
Another note: If you have a scoring set-up where you add a score, wait x days, and then remove the score, you may have a very recent behavior score - but at the same time your flames in Sales Insight will be off. Since the flames are calculated based on recent activity, your decay can erase the scoring gain made in the same time, and keep your flames to zero - despite the activity. That's why I favor the score decay after a longer period of inactivity.