It is if you can get a version of 10.6.8, which isn't available directly on a disc AFAIK. There are various interesting ways to achieve that - easiest is probably to set the iMac in Target Disk Mode and run a Firewire cable to a host computer that you can run 10.6.0 on. Then boot install the OS on the target disk and reboot the host from the target disk. You can then upgrade to 10.6.8 in the usual way, shut everything down and finally boot the new iMac into SL.