This ^^ - If you fish long enough with enough different jig heads, you'll see the difference. Not that you can't use others, but mushrooms definitely seem to be best overall, at least for the conditions the technique was originally created for.
Technically, no. Depends on how close you want to stick to the "original." Elaztech is the material in Z-Man baits, as well as the Strike King Ochos. Other baits will fish and react differently being made of a different type plastic material, as well as differences in salt content or addition. They will all catch fish, but the best thing for anyone who wants to try Ned Rigging is to first begin with the exact original setup, Elaztech plastics and light (1/32, 1/16, 3/32) Gopher mushroom head jigs. Once you've fished those and learned how they react and why they work, then you can start playing with all the different component alterations that are possible. But until you have fished with the baseline rig, you'll have no basis for comparison...only another similar version that you won't have any idea why it's different than Ned's original setup.
-T9