Can a merchant using Square Register accept bitcoins? Square's marketing department appears to be successful at convincing some retailers to chuck their old register and instead buy an iPad, receipt printer and cash drawer and use the Square Register app instead.

Can this same set of hardware be used to also accept bitcoin payments?  Is there an app for accepting Bitcoin payments that will work on the iPad?  If so, can multiple apps run simultaneously?  Could the retailer print some type of receipt?

[Assuming the Internet access is through a Wi-Fi access point.]
Bit-Pay has a mobile app that allows acceptance of mobile payments. It's not native for the iPad, but it should work, albeit at a lower resolution. There are a few other iPad apps, but none that implement any sort of payment functionality.