When talking about the atmosphere of a record, I don't really take the specific lyrical content into account. "Raining Blood" though does have a kind of evil feeling to it, with the tension built by the intro for example. But I think the feeling of Reign in Blood comes almost entirely down to the terseness of the album's length as well as the intensity, aggression and violence of the compositions.
It could be an album based around a concept of eating cotton candy and it wouldn't change my feelings about it being aggressive and violent rather than evil. Of course this is also relatively speaking because it would sound evil by comparison to many other albums by other bands.