Yes that is totally possible...
There is no official API for it but check out the source code to this project:
https://github.com/liamnichols/iBeaconScanner
It shows how you can listen out for BLE devices broadcasting using the iBeacon Protocol in the area using CoreBluetooth.
Hope it helps
Edit: Although a commercial app might need to implement its own kind of advertising protocol instead of trying to piggy back off the iBeacon protocol... If you want to understand how the advertisment data for the iBeacon works, check out this answer: https://stackoverflow.com/a/19026387/814389 It shows the structure of the packed being advertised.