As much as that appears to be a bug, that actually looks kind of cool! I saw someone running around with the Omega armour lower half complete with grenades, and a mirror-universe "sports bra" on the top, and it looked pretty boss.
I think this bug comes down to the fact that the Fed-only and KDF-only STF costumes were never meant to go on the opposing sides, and because Gorn have particular chest and head meshes, these probabbly conflict with the MACO chest armour mesh... or something.
have you experimented much with swapping the uniforms and visual states.
I ask because I tested the maco MK XI on my two Orion diplomacy officers as well as my gorn and they worked correctly(on tribble two patches ago).
Also its possible your Gorn has studded in at the school of Kirk and is of the opinion that shirts are superfluous.