Ideally, the evaluators would be disinterested third parties. But if disinterested third parties aren't stepping up, charities evaluating themselves is a heck of a lot better than nothing.
And disinterested third parties are by definition not controlled by charities. So unless charities have some kind of guarantee that someone they trust will be studying their effectiveness, they should absolutely run evaluations of their own programmes.
Consider: if GD wasn't evaluating itself, this conversation wouldn't even be possible. And while I'm not sure who's right here, I'm confident that the discussion is worthwhile.