Both of them use ARM.
The iPhone is a combination device that has a different processor architecture than the iPod. Then you have to consider memory on the two devices. The iPhone probably has ~512MB onboard memory for the system while the iPod might have ~16-32MB.
EDIT: These are just assumptions and mean nothing in terms of specs.
More importantly, who knows if the current iPod isn't running OS X ?
Apple never made public the OS of the iPod (except for the first generation ones, which used Pixo)