That's true, only NZ's is called the Haka.. but Fiji have the cibi, Tonga have their version (i forgets the name) and Samoa have the Siva Tau.
If you looking the gamefiles, there seems to be a random file named NZL , which probably is for NZ's haka.
I am wondering if you duplicated this and edited, then you could actually make samoa, fiji and tonga do the haka. Ok it's not perfect, but it'd be an improvement.