How to install Snow Leopard from USB where USB disk is prepared using Linux?
Why use Linux for this? Just do it in OS X. To prepare the USB drive (e.g. 8-GB flash drive), you need to partition it using the GUID scheme and format it to the file system standard 'Macintosh Extended (Journaled)', also known as 'HFS+ (Journaled)'.

Then use Disk Utility's Restore feature to copy the contents of the iso image file (Source) to the USB drive (Destination). When done, restart the Mac keeping the Option key pressed – the USB drive should then show up in the boot volume lineup... 

There are many tutorials for this process on the Internet, e.g., http://www.maciverse.com/install-os-x-snow-leopard-from-usb-flash-drive.html