Great question! Yes, you can use an external scanner to read a barcode into a data capture or signoff field. A barcode scanner will act as a keyboard wedge, meaning it will read data and then enter it in as text wherever your cursor currently is. This is a little friendlier when using a laptop or desktop computer, but it may be possible to use a barcode scanner that connects via bluetooth to a phone or tablet.
Using the device’s camera would be trickier. This would require leaving the Dozuki site or application, opening up a 2D barcode/QR code scanning app, copying the text information, and then pasting that information back into Dozuki. This probably isn’t the best solution, however, because it sounds like you’re trying to address the tedium of repeatedly typing in responses/passwords. This may just create more work than it eliminates.