Evil defined as the absence of God is not an unusual definition. God is good, so where goodness is God is also. You do not need to acknowledge God for God to be with you and act through you. Of course atheists are not evil. We all have both good and evil inclinations, and hopefully good wins our hearts most often, no matter what our philosophies, religions or worldviews are.
It may not be uncommon to define good in terms of God, but it does put the person defining things that way in the position of having to come up with valid support for Divine Command Theory.
... however, I suspect that most people who do define morality in terms of God and then go on to use this as the basis for other conclusions do so in settings where that logical leap in their premises isn't questioned.