Ok, I wasn't 100% sure I understood your question, but I think I do, so here's a stab at it:
There are a couple ways to access the errors of a child form, but all seem to need the name of the ngForm.
Assuming this structure:
<form name="parentForm">
<ng-form name="childForm"></ng-form>
</form>
you know that you can access it via $scope.childForm.$error, but less known is that it is also attached to the parent form. You can access it with $scope.parentForm.childForm.$error, but obviously, that's no good, since you still need the name.
You could get hacky and loop through the properties on the parent form and try to tell which one is the child form and go from there.
Lastly, as we've discussed on Twitter/GitHub, I have a directive that kinda does some of this magic for you. It did have a bug that didn't handle embedded forms correctly, but I fixed it. Check out the new version of my directive that tries to simplify handling errors with Angular:
https://github.com/CWSpear/angular-form-errors-directive
I added the ability to display all the errors of all the child ngForms with a flag in v1.3.0.