All are different in terms of most of the skills needed to do any of them.
The One Wheel is much more like a snowboarding in soft powder than it is like skateboarding, but even then, it's not quite the same. There's a sort of softish center pivot feeling, where on a snowboard it depends on where your edges are.
Skill wise, you don't need any to make the One Wheel do what's advertised. You do need skill to ride it confidently, but you gain those skills as you use it.
I've had one very bad fall on the One Wheel, and it was bad. It slide out while going fast down a steep slippery/sandy hill, and then nosedived, which sent me cart wheeling, then whipped my heel into the ground, shattering it into 23 pieces. I was in bed for 6 months, and didn't walk without help for 12.
I actually think my other boarding skills made the injury worse. I reacted as if the board was a skateboard, where a sideways slide is something I'm super comfortable with and do on purpose. That reaction was to lean deep, counter to the forces of the slide. The big fat gripping tire of the One Wheel bit in, then acted as a fulcrum with my body as the lever, and I just went sailing.
The advice from the GP to have One Wheel-curious people try a skateboard first is indeed good advice. It won't teach you how to ride a One Wheel, but it will teach you how hard the ground is.
