This is a question for those of you who believe morality is a product of evolutionary forces acting on the individual, and also on a group level through group selection.

It provably is, but I'm guessing that won't mean much to you.

Are they not perfectly justified in pursuing what they, as a group, believed to be right?

First off, you're confusing good belief and good action. If Bob believes that murdering an innocent person will save the world from an evil unicorn apocalypse, then Bob's action is 'right,' since he is trying to save the world. Bob's belief is wrong, since it is stupid and far-fetched. You need to have good beliefs and good actions for your decisions to be moral.

Second, right and wrong (in the context of moral beliefs) are words we use to describe things we don't like. Very few of us want to be murdered, so we construct a society where murder is illegal. The basis for condemning genocidal maniacs is (obviously) our subjective morality.

Now, the funny thing is, you seem to be under the impression that there is an alternative to this, that there is an 'absolute moral truth' we could use instead. Unfortunately for you, there is no consistent way to discover this 'absolute' morality. In fact, every codification of ethics is provably man-made, and so choosing to call one such moral system (eg the bible) 'Absolute' is merely the decision to stop questioning your subjective moral system.

It seems to me that you can either uphold their actions as morally sound, or condemn them. And by condemning them, you appeal to some standard beyond "group" think, that makes your position right, and theirs wrong.

First, even if there is an 'absolute moral standard,' you have no way of condemning them either. Unless Germany had free and unrestricted access to a coherent absolute moral code, then they were still acting according to what they thought was right, and so you still can't condemn them if you think like in the OP. Obviously they didn't, and so if you want to condemn them, you can't appeal to an absolute moral code.

Second, whatever you might think, our moral judgements don't rely on appeals to authority. Morality is something we can only figure out for ourselves, and having done so, we can only trust ourselves and our instincts.

Subjective morality isn't a perfect system, obviously, but it is literally the only system we have.