Honestly, they shouldn't be able to 'jump the gun' because they are under the same cool downs that you are. Medica II/pulling with regen on is really the only thing that should be pulling hate off of you before you can get your first RoH combo off.
I understand your concern here and the DDs don't have to be dicks about it; but I would look into your opening as well if DDs are actually pulling hate off you at the start as there is some room for improvement on your side.
Obviously them attacking a different target than you at the start would be exempt here.