The ROM chips are completely different. Have a look at
NES ROM Pinouts.txt
UNROM uses a 28-pin DIP 128Kx8 Mask ROM, whereas the UOROM boards use a 32-pin DIP 256Kx8 Mask ROM.
All of the above is assuming you are using donor boards. If you are talking about using RetroZone's reproduction boards then yea, they are the same. Just make sure you use JEDEC-compatible ROM chips.