It’s not that ridiculous. We had an airship in Athens during the 2004 summer Olympics [1] which was specifically used for surveillance reasons. Of course there were no UAVs back then.
Oh, there were - just not in the public consciousness. Rotomotion was selling them for one, and they led the Autopilot open source project to create a platform for single rotor craft.
[1] http://www.swissinfo.ch/eng/blimp-plays-big-brother-at-the-o...