No. Atheism is itself a mortal sin, and the worst sin possible to commit besides the One Unforgivable Sin, worse than genocide.
Atheism is a violation of the First Commandment of course, but moreover a violation of the Great and Foremost Commandment that includes that commandment. The Great and Foremost Commandment is the most important commandment of all, and infinitely eclipses all prohibitions against sins committed against one's neighbor. Both of these commandments are part of the Noahide Covenant, binding on all of humanity, not just Hebrews or Christians. All atheists are thus by definition gravely immoral in the worst way that it is currently possible to be in this world. God forgive and have mercy on them.
Besides those sins, I've never met an atheist who shunned every other sin and vice and embodied every virtue (things like Faith obviously excepted which is by definition impossible for them to embody). And I've known well perhaps fifty or so atheists in my life. None of them are as righteous as they could conceivablely be while still remaining atheists. I can't think of a single one who didn't engage unrepentantly in some particularly odious sin either privately or unashamedly.
Thus I answer, no, atheists are not and cannot be moral people unless they cease to be atheists. Atheism is evil in itself. Nor are atheists moral people apart from their atheism. They aren't, which can be seen from their public behavior, but could they conceivably be? You might as well ask if anyone can be a moral person, then. The answer to that might surprise you.
Thank God a good number of atheists are in a state of ignorance and subject to other mitigating factors. They are not beyond God's mercy and ability to save. A good number of atheists will convert. I am a convert from atheism myself. Praise God. We must show love and kindness and mercy to our atheist neighbors. They are sinners, but so are we.