From what DMcCoy seems to say, it appears to use the domain name of the IAS machine as the domain of the devices. Which would make sense.
2. So you mean, AD will authenticate a user ( a printer in this case with its mac address being passed on to IAS by switch as both username and password) even if it presents only username / password and no domain name?
Yes, they need reversible authentication on the MAC address accounts for all devices that will authenticate via IAS.
3. I think I could not explain this better. I meant to ask if mac address accounts that I will create in AD, will these be required to be stored as hashed MD5 as there is an option to check or uncheck this on user accounts while creating passwords.