I tried out some stuff to possible run the Exploiter Orb faster, and tried to build a Mirage build to work together with my Catchmoon kitgun and had to find out, that my kitgun does NOT receive any additional damage from Mirages Eclipse ability.
I tested it in the Simulacrum, with lvl 115 Prod Crewman (for the screens) and several other enemies, all with the same result
Normal Arca damage
Buffed Arca damage
Catchmoon kitgun (Catchmoon + Haymaker + Splat)
As you can see, both times the damage is the same, while other weapons or a Thombfinger Kitgun doesn't have that problem and get a nice boost in damage.
Chroma has the same problem with the Catchmoon kitgun, every weapon I tried got a boost from his Vex Armor buff, but the Catchmoon still deals the same damage.
Will provide more information if neccassary