Yes. We DO use auxiliary verbs for affirmative statements - as this sentence demonstrates!
If you want to add emphasis to any statement, insist that something is true, contradict something that someone else has said, or simply say something heart-felt, you can use the auxiliary 'do' or 'did'.
The first sentence in this answer is a typical example. You expressed some doubt as to whether or not the construction was correct, and I assured you that it was by using the emphatic 'do'.