The front of the lats can be hit with both dumbbell and barbbell pullover. But a good pullover machine stimulates the growth even better i think.
The resistance is only in the stretched position when doing pullovers with db/bb. There is no resistance on the lat in the contracted position. In fact, you don't even get the lats in a contracted position.
As you stretch back with a db the lat takes the full resistance as free weights only apply force in an up and down position. As you start raising your arms your triceps and chest starts to support the load in an isometric fashion. In the finished position, your arms are in front of your chest and you are supporting the weight with your pecs, front delt and triceps -- like the beginning of a bench press.
Not only is their no resistance on the lat in that "finished" position but you still have another 90% range of motion for your lats. Full range defined here is elbows/upper arm starting behind your eyes and moving forward in a rotary motion ending the elbow/upper arm slightly behind your hips.
In one of Jays videos where he is training chest he includes db pullovers for chest. The chest muscles
start supporting the weight right about when you arms start passing your forehead.