For the purpose of this conversation we'll define skeptic as: "a person who maintains a doubting attitude, as toward values, plans,statements, or the character of others."
So are atheist skeptics? (Not necessarily in relation to God(s) but in general.)
I would say your chosen definition of 'skeptic' has no relation to atheism in general. This type of ordinary usage connotation can apply to anyone, and is more of a general, doubting personality type.
However, 'skeptics' in regards to the philosophical connotation of skepticism being "a mode of inquiry that emphasizes critical scrutiny, caution, and intellectual rigor," do tend to be atheists, as atheism is a general conclusion resulting from such an approach regarding knowledge.
Of course, all atheists are not skeptics of this variety either, as people can identify as atheists for a whole range of reasons and motivations.
It's good that you defined your terms, as this is rare occurrence with most people, which, inevitably, results in nothing but arguing over semantics while people talk past each other. Of course, I would say that the second usage of skepticism is what people are usually talking about when it comes to religious belief and atheism.