I have not seen skarsnik faction nor 2 generic Greenskins faction pop their Waaghs in battle.
To confirm the AI got to 100% Waagh bar, I restarted a Thorgrim campaign and used the additional stats in FFA and domination mod, which shows Waagh percentage, and it reaches 100% yet the AI never used it in battle.
I have not seen skarsnik faction nor 2 generic Greenskins faction pop their Waaghs in battle.
To confirm the AI got to 100% Waagh bar, I restarted a Thorgrim campaign and used the additional stats in FFA and domination mod, which shows Waagh percentage, and it reaches 100% yet the AI never used it in battle.