The URC-200 wasn't originally designed to work with the
MRF-250. The fact that the "0" address is an open address
took place afterwards. As Edmund said, it will work with
it, but you will not get the complete functionality of
the MRF-250. It will act just as an MRF-100 would.
Is there a chance that there are some MRF-250s that
don't output anything on address 0? When I set mine to address 0 (and set my MX-850 to use address 0), the MRF-250's LED blinks when I press a button on either the URC-200 or the MX-850, but the component doesn't do anything (i.e. it looks like no IR output is occurring)...
I'd hate to have to buy another RF base, just to allow the URC-200 to work, as I already have an RF base...
Jason