DataWedge docs are here if you have not seen them. Make sure to select the right version.
Not sure what you mean by allowed-apps list. There is a Disabled apps list. If you have added your app there, the scanner will be disabled when your app is in the foreground.
You can create a profile for your app. If that is what you are doing, when you add your app to the "Associated apps and activities" for that profile. Make sure you select * for all activities in your app or individually select all of the activities in your app that you want the scanner active in.
You could turn on the logging in DataWedge and then look at the logcat logs. You will see events like this when DW detects a new foregound activity and turns the scanner on or off based on that.
08-22 15:49:35.188 4327 4327 D ScannerPlugin: ScannerPlugin.enable() for profile : chrome