because the things you describe usually have OS dependant drivers you would need to look not just at Air but possible the new Air 2.0 features which allows you to run flex as a native OS application.
. But before implementing anything be sure to check the devices you intent to support drivers!! We've successfully connect Ingenico and Verifone Credit card/signature captures and I'm sure the API support drawers.
The Scan Guns we've used are mostly KeyboardWedge so there is no need for hardware communication, just a good handling of the focus in the app.