While I haven't personally set my iMac up like this yet I can say with confidence that it SHOULD work as the startup disk location is set in the OS.
Apple has a [http://support.apple.com/kb/PH6656|KB article] detailing how to change/select a startup disk for your Mac to boot from. Assuming you've already installed the secondary drive and installed an operating system to that drive, these will help you boot using that drive:
# Power the Mac on while holding the "option" key on your keyboard
# After a few seconds a gray screen should appear with one or more hard drives visible. Any attached hard drive that has a bootable operating system will show here.
# Select the desired hard drive and click "return"
# Once the Mac boots to the operating system, open System Preferences
# Open Startup Disk
# Select your desired startup disk
# Click restart to finish the process
Your Mac should now default to the specified startup disk. If you need to change it in the future you can use the "option" key method to temporarily do so or the System Preferences method to permanently do so.
Hope that helps!