Durge wouldnt be able to attack while Ventress and Grievous come in close, so thats one opponent he doesnt have to worry about at the moment.
Grievous can be pushed away with the Force, giving Dooku time to focus on Ventress.
This gives Dooku one on one against Ventress, unless Durge interferres. Should be an easy victory for Dooku, so lets just say he kills her.
By now, Grievous is up and coming back in, and Durge wouldve fired off a few rounds. Dooku should be able to parry lasers easily, so his problem would be rockets.
Grievous would fall, he doesnt have the Force to rely on and Dooku would know him like the back of his hand.
Dooku vs Durge left, Durge has the upperhand in this battle as long as Dooku cant get close to him, but Dooku has the darkside to use, so I think he'd take out Durge eventually.