A traditional hovercraft doesn't care what the terrain is because it's basically a leaking balloon and has sensible limitations as a result of it's design. You force air under the object and lift it from the ground via pressure, the pressure needed to lift it increases with the amount of pressure from the mass. The extreme weight limitation in order to maintain a low pressure is the only thing that allows float on water. Whether a hovercraft can float on water is simply a question of whether the thrust required to create that pressure differential is more than the thrust required to displace the water beneath the object instead.
If you're using some sort of futuristic tech where you're doing something different to keep yourself afloat instead, even if it followed the same rule as modern hovercraft it would be extremely unlikely to be an amphibious vehicle and still be an effective combat vehicle. If whatever force that keeps them afloat would simply bore through the water under their weight, they can't be amphibious. Modern hovercraft aren't used as combat vehicles for this reason, they're landing craft where used, as anything that floats on water and carries weight is already by nature somewhat fragile to start with.
A futuristic hovercraft capability of significantly higher thrust, that was capable of supporting a heavily armored war machine of massively high density compared to naval vessels, would be a means to a smooth ride, not amphibian capability. If it was capable of achieving a bit of elevation, say a few meters, it would be an extremely all terrain vehicle. You can't drive a tank through a mountain range or a river, with a three meter clearance you could cross most of them on this planet with little trouble. With just a meter it would put tracked vehicles to shame.