Does FreeRTOS support SMP systems? How does this affect porting?

Erich,

FreeRTOS is certainly capable of supporting SMP. The porting, however, is left as an exercise to the one doing the porting.

Seriously though - you can use FreeRTOS as the underlying OS - you'll just have to figure out the communication protocols, etc.
yourself between the respective PU's (processing units).

Regards,
John W.