Newton and Galileo were certainly Christians, but Einstein was agnostic... and atheistic with respect to a personal God.
Newton was a unitarian - he didn't believe in the divinity of Jesus. I'd argue that pretty much makes him not a Christian - it certainly makes him fundamentally opossed to the views of nearly all living Christians.
Christians can be scientists, but creationists aren't scientists because creationism isn't science, it's dogma.
Creationists can be scientists, there have been some very fine scientists who are creationists - although none in biology. What there cannot be is creation science.