Whoever told you it was Horse Hoof fungus is mistaken.
It's common Ganoderma, often called Artist's Conk, as someone mentioned earlier.
And yes, you can extract amadou from it (I have). You won't get as much as from Horse Hoof but it is still there just a much thinner layer. Cut down into and you're after the tobacco coloured velvety layer.
Personally I've always thought amadou was more trouble than it's worth. Never could understand the bushcrafter's fixation with it. Char cloth is much easier to make and more reliable. Ho hum.