There should be no "hatred generating" and "hatred spending" skills, only Hatred and Discipline. As the DH uses more hatred skills, the gauge shifts up to the red. Using Discipline skills will shift the balance down to the blue. The current balance level will dictate what skills are available to use.
When enemies are near, the gauge should slowly fill with hatred at a rate proportional to the number/difficulty of the enemies, symbolizing the DH's intense desire to kill demonspawn.
In town or at times when no enemies are near, the gauge should slowly shift towards discipline, symbolizing the DH's calculating personality which keeps him alive.
An interesting twist would be to apply bonuses and penalties to the DH depending on his current balance of hatred and discipline (example: At high hatred, the DH's attack is increased but precision is decreased and he cannot use potions)
Here are some reasons why I think this would be a better system: