I have heard this story a few times before.
A barbarian army runs up and slits their own throats in an attempt to scare the enemy - This could alternatively have been something that they made their prisoners do.
I'd like to know if this 'story' is true and which historical military faction did this if so.
What you have said is partly true, yet partly untrue.
It was the army of the Chinese King Goujian of Yue who lived circa 500 BCE, ruler of the Chinese State of Yue during the Spring and Autumn Period (which spawned from 8th Century BCE-5th Century BCE)
King Goujian's army was known for scaring its enemies before battle by forcing its front line, composed of criminals sentenced to death, to commit suicide by decapitating themselves.
Sima Qian, Shiji (史記), Ch. 41, 中華書局, 2006, p. 272
Another possibility would be the Balinese puputan (there's not much good stuff on the internet, but the wikipedia link is reasonably informative). The term is used for a number of events, the death of the Raja of Denpasar in 1906 being fairly close to what you described. As the Dutch arrived at his palace, the Raja, along with his wives, officials and whoever, walked out of the palace, almost up to the Dutch, and began killing themselves and each other. This blog has a contemporary account of it. The word is also attached to the far less ritualised suicide of the king of Tabanan and his son in prison, and to the 1946 battle of Margarana, where it refers to the fight to the death (rather than suicide) of a number of Indonesian soldiers under I Gusti Ngurah Rai. Unfortunately English sources on this are even rarer, but it seems that Ngurah Rai called the battle a 'putuputan' himself before he died, so it's not just resistance in the form of direct suicide like you're asking, but some events like that did happen.