When it comes to evolutionary adaptations, we can only have insight or theorize as to how things got to the way they are. As for the lack of feathers, yes, it is "suggested" that they lost their feathers on their heads so as to access the inners of a carcass without having the mess stick to their feathers and invite bugs or bacteria to fester. Again, there is no real proof for this other than studies done via means of statistics etc.
Live critters.....hmmmm??
Well, let's just say this: I've heard of ranchers complaining of calves being picked up and taken away by eagles. Those old stories gave lots of people hearsay reason to shoot LOTS of eagles. If you know the weight of an eagle vs. the weight of a calf, it only makes sense that this isn't true. As for the vultures; I've never head of it but anything is possible I guess......especially when motive is involved. Lot's of eagles died for these reason. Nonetheless, I haven't witnessed vultures killing, nor have an any data to support that they can or can't do it either, so I can't say. I do know that their feet are not capable of grasping which does not support any means of attacking a living animal...but again, ya never know???