Hi,
I have been running tests with android and iphone, and my unofficial answer is that certainly you can. I have found out the following:
Have the WordPress backend open in your mobile device.
For android you need a separate program called Barcode Scanner. And after you have scanned then just follow the link and it will do the trick.
For iphone you dont need any qr-code scanner. The iphone camera will detect that it is qr-code and will try to open Safari directly. Follow the link and it will make the check-in. So use your camera in Ios.
It goes smooth with ipad or android pad as well. Android is neat at will make a sound as the code is read. So it will kind of notify your customers that you are really doing something. Maybe i could make a sound for it in iphone as well, but have not investigated this. Let me know if you find out how to do this.
just do it!