No, the Command 8 control surface will not work with FCP directly. It's needs to see Pro Tools hardware.
The M-Audio/Digidesign ProjectMix I/O recognizes the Mackie Protocol, so does work with FCP 5. The ProjectMix I/O also runs with Pro Tools M-Powered (sold separately), so if needed, you can work with either.
http://www.m-audio.com/products/en_us/ProjectMixIO-main.html
The Yamaha 01X which Jerry noted, also has the advantage over the M-Audio as being a standalone mixer and costs less.
...Tom