They can only be used as "micro-surveillance tools" once you install an app that shares your proximity to a beacon with a remote server... and by installing a 'malicious' app you've already lost.
WiFi is active and yes, wiretapping is possible, at least for locating you. Hardware/software for doing this though is not readily available as far as I can tell.
Finally, iBeacons: very simple software running on a passive BLE device that simply records all BLE UUIDs passing by, that's all!