I know the the discrimination of a ROC curve is optimal when the curve goes through the top left corner. But does this also count for the bottom right corner?
Yes it does count for the bottom right corner. If the ROC curves inwards perfectly to the right corner it means you've got your results inverted but you are still correctly identifying all TRUE positives(but calling them FALSE) without any FALSE Positives (all your TRUE negatives are called TRUE). You just need to invert your results, i.e. convert all your FALSEs to TRUE and TRUEs to FALSE.