You cannot boot a 2012 iMac from Snow Leopard. That old version of Mac OS X does not have the drivers for the newer hardware. If you need to run Snow Leopard to be able to use older software, you can buy a copy of Snow Leopard Server from the online Apple Store for US $19.95 and run that in one of the virtualization solutions (Parallels Desktop, VMWare Fusion, or VirtualBox).
Can I use the snow leopard OS with this iMac?
Yes, as varjak paw described, but you cannot obtain Snow Leopard Server from the online store, you must telephone them at 1.800.MYAPPLE (1.800.692.7753) - Apple Part Number: MC588Z/A. (varjak - am I wrong here; you obtained a copy online or found an online link? Please update us to the URL...)
I assume that you want to run Snow Leopard on your new iMac so as to regain access to Rosetta and run older PowerPC software. If not, please be more specific.
Here is Adobe's Creative Suite 2 (CS2) Photoshop running in SLS in Parallels 8:
[click on image to enlarge]
NOTE: Computer games with complex, 3D or fast motion graphics make not work well or at all in virtualization.