I'm not familiar with the radio code in Rockbox, but currently Rockbox supports a number of regions including Europe, US / Canada, Japan, Korea, Italy and Other, so there is flexibility.
However the limitation will be the chipset used in any particular player, which might explain why there doesn't appear to be support for the OIRT region (at least not in the Sansa e200v1).
http://en.wikipedia.org/wiki/FM_broadcast_band indicates that the OIRT FM broadcast band covers 65.8 to 74 MHz.