Joveth Gonzalez went on the forums today to inform us that companions will be able to wear the Gree armor in a future patch.
Companions Cannot Wear Gree Armor | 02.20.2013, 04:25 PM
We’ve updated the Known Issues to reflect that this is, indeed, not working as designed. Currently, companions are unable to equip gear that has a Reputation requirement, but this will be resolved in a future patch. Once this issue is resolved, you’ll be able to use the gear as intended on your companions.
Joveth Gonzalez | Online Community Manager