I think they took a Snow White cartoon and manipulated it to be in same position she was in. Perhaps the eyes were off a bit. She has all the components, and they have costumed her perfectly.
I've seen lots of photos of her that she is very snow "white" so I imagine with lighting it works. I mean I am full Euro (mostly Irish/English) and she is lighter than I am. Overall I don't think it matters about skin color but in this particular part she is called Snow White because her skin is so light, like snow. There is a happy medium it can work.
YES! One thing I think is important when going from Cartoons to Human is bone structure. Snow White has a unique look and I think Rachel has the perfect bone structure. I think it's a great casting.
And regarding Ariel, I think the most important component was red hair, and she has it. But if you look at Ariel's bone structure (it's bold) and nose shape ~ Hailey has the perfect structure, nose and lips. Love this casting too!