Nope, they shared the same cooldown and it wasn't fluid, for example you would select a buff and be locked out for a short peroid before you could select the attack, I assume now you can select a buff and attack skill without the break in between which will make combat more fluid similar to other MMO's.
Huh, that's not what I remembered it being.
What I remembered was that during GCD, you couldn't select anything (buffs or attacks), but otherwise you could select buffs immediately followed by another buff or an attack.
But I'm probably misremembering.