They have pretty much the same meaning, but I've noticed soft differences in the way people use both.
You will hear "Não é mole.
", without anything afterwards less
than "Não é mole, não.
" or "Não é moleza.
". It seems like if you say just "Não é mole." you are talking about food.
That's what I have realized, it may change according to diff. places.
See ya, Thomas.