From Codex:
“Rage +X (Object Trait)
When wounded, this creature becomes extremely vicious and aggressive. Each time it is attacked and damaged by an enemy creature, place a Rage token on it. It cannot have more than X Rage tokens on it. It gains the Melee +1 trait for each Rage token on it. Each time it heals or regenerates, remove 1 Rage token. If it has no damage on it, remove all Rage tokens.“
Also from Codex:
“Enemy (Game Term)
An enemy object is one which is currently controlled by your
opponent(s).“
The interesting word is enemy. Each time it is attacked and damaged by an enemy creature... So friendly creatures doesn't count. The mage out this group of Monkeys cannot hit themselves. I guess DoT attached or effected by friendly will also not work I guess. Seems like you have to wait till somebody hits the gorilla three times.