Before going on and on and on about the Allied ship thing again, look at all of your own characters. Do they use allied Ships/Weaponry/Equipment? I highly doubt that everyone has say, for example, Full Kusari or Libertian loadout.
If your a 100% purist, then think of this. The GC can use the Catamaran. If their smart, they will use the Catamaran during this version's period. Their allowed, its a good ship, and their great pilots. Hell, we even roleplayed it a while back that the HG would bring them a certain number of Catamaran's in exchange for Griffin's. So even that's covered.
I personaly see no reason why you should continue on with discussing the Catamaran.