Well, I don't know about scaring the Germans away (it is unlikely the Germans would have let them finish such a performance had they witnessed it first-hand), but during WWII the 28th (Maori) battalion of the 2nd NZ division would fairly frequently perform a war haka (peruperu) before combat (there are a number of different types).

Mentions of haka abound in accounts from WWII combat.

From the battle of 42nd street on Crete (from the history of the Pakeha 19th battalion, from the same brigade as the Maori):

During this period enemy ground forces managed to get up close without being seen. A sudden burst of spandau fire from some 300 yards out in front indicated the start of the attack. This fire was also the signal for the Maori company detailed for the counter-attack to start their traditional war haka. Here was a task to their liking; led by their company commander, waving a very dirty towel, they moved through 19 Battalion’s area and unhesitatingly crossed the sunken road just in front of Taranaki Company. No. 13 Platoon Hawke’s Bay Company, over whose positions they passed, held their fire for a moment then, inspired by the Maoris’ example, joined in also. Soon the whole force in the vicinity were fixing bayonets and following up ... The Hun, despite his vaunted superiority, was no match for this miscellaneous group of New Zealanders and Australians who confronted him with bayonets. There were no prisoners taken; this was mortal combat. In front of the determined advance the enemy broke and fled, leaving behind him many dead and abandoning his arms and equipment as he went. He was driven back about half a mile and lost probably 300 men

http://nzetc.victoria.ac.nz/tm/scholarly/tei-WH2-19Ba-c10.html

Probably this is the example being discussed, since it was very much an 'ANZAC' attack - the battle of 42nd street being a famous incident from the battle for Crete.

Minqar Qaim:

I can still see Lt Hupa Hamiora10 out in front of B Coy prancing, leaping and yelling as he led that famous haka Ka mate! Ka mate! No opposition was met by A Coy. We passed clean through the enemy defences (not manned), arty and troop carrying vehicles. The drivers of these were in bed either on or under their vehicles. When there was no more opposition the red, white, green success signal was shot into the dusty sky and the brigade sorted itself out and re-formed. There were no prisoners to worry about and the men with reddened bayonets cleaned them in the sand while waiting the arrival of transport. A watchful eye was kept on the rear and flank in case of counter-attack, but the first battalion of Rifle Regiment 104 had been practically annihilated by 19 and 20 Battalions and the few survivors were heading due north as fast as their trucks could carry them.

http://nzetc.victoria.ac.nz//tm/scholarly/tei-WH2Maor-c7.html

Alamein:

We had to fight almost every inch of the way. We were never far behind the barrage which gave us good protection and did some damage too…. At one spot we were opposed by a wall of enemy firing at us with all they had. We all broke into the haka “Ka mate! ka mate!” and charged straight in with the bayonet…. It was the most spirited attack that I myself had taken part in.

http://nzetc.victoria.ac.nz//tm/scholarly/tei-WH2Maor-c9.html

You can read their (28th battalion) WWII history here: http://nzetc.victoria.ac.nz//tm/scholarly/tei-WH2Maor.html

Visit their (sort-of) official website here: http://www.28maoribattalion.org.nz/

Watch a performance of the most commonly performed (by the 28th) haka (though it may be more accurately called karakia, or 'sacred chant') here: http://eng.kiamau.tki.org.nz/Multimedia/Company-A/Rendition-of-haka-Ka-Eke-i-te-Wiwi

Also, does anyone know where I can learn that particular haka?

Opinions on the performance of haka by non-Maori and non-NZers are mixed, to say the least - please approach it with caution and respect.

Kia Ora , Maori Battalions in WW1 and WW2 incorporated scare tactics but i believe it wasn't the Haka their opposition was scared of. From what Ive researched, it was their aggressive hand to hand combat but mostly their head hunting scare tactics that the Germans and the like feared most. The Maori Battalion recorded more Kills from hand to hand combat then kills from using a Gun. They were mostly put in the trenches for digging and hand combat, as trench warfare was how the tribes had been fighting in NZ for hundreds of years. Head collecting and cannibalism was normal for Maori , even in the 1900's it was still practiced, tho not mainstream like it was pre-european times. Some soldiers in the Maori Battalions would parade around the decapitated heads of their enemies and put them on spikes popping up out of the trenches. Collecting heads showed your Mana and prowess. Though ive found no accounts of cannibalism for the maori battalions in ww1 or ww2 , i wouldnt be surprised if they slipped in the odd human heart with their boil up stew.