Having to use the camera barcode scanner in landscape only isn't an issue with the ABZxing library, it is the scanner app settings. Try quickmark if the one you use doesn't allow portrait.
Can I make QuickMark as the default app to download?
When a barcode scanner is not available it automatically points you to download ZXing barcode scanner. Is there any way I can select QuickMark as the default barcode scanner to download instead?