PoH's cannot make Nobodies or Heartless. In fact, PoH doesn't necessarily mean that the heart is strong- just that the heart has no darkness.
So they cannot make Nobodies.
Anyone makes a Heartless if they have the necessary darkness. The stronger the darkness, the stronger the Heartless. Anyone with a strong heart can also split into a Nobody once they lose their hearts.
Now, those with the strongest hearts make up the Organization- they're not mindless drones, they just can't feel. They're able to think and they retained the memories of their Somebody, except for in Roxas' case. I think that the reason they're able to retain a body shape and thoughts is because of these memories- we certainly don't see Dusks saying that they have memories.