I have bought several knives from the US without problem. Customs have good information on their website about what is not legal in Australia, Customs Officers enforce the rules, they don't get to make them up as they go...
Essentially, a "folding" knife is legal provided it cannot be opened with one hand with a flicking motion. A Spyderco folder for example can be opened with one hand, but cannot be opened by inertia acting on the blade by "flicking" the knife with a rapid hand motion, so they are perfectly legal. Lookie here for the test: https://youtu.be/NthM0-j76AU
Ceramic blades are illegal because they can pass through X-ray machines without detection. Butterfly knives etc are also illegal, but if your just buying a survival knife, a good quality hunting or folding knife, you should have no problems - I never have I have imported numerous knives.
Edit: just saw the knife your referring to, Zero Tolerance ZT0804CF. There should be no issues whatsoever with that blade. I imported several Falkniven A1 knives, no issues.