If you're new doctor is familiar with 'comorbidity' you should do fine. It's a fancy word that means that ADD often 'comes with' other disorders; such as dyslexia, depression, OCD, PTSD, and other acronyms and scary words
So, you are on to something...treating the ADD often improves the symptoms of whatever disorder is comorbid with it; however, sometimes you have to treat both. So, if your Doc understands that (and you do to) you'll start off treating the ADD and after time evaluate the symptoms of the secondary disorder and determine if further treatment is needed specifically for it, or if it has moderated enough to not be an issue.
I wish you the best...and once you have a good doctor, don't let go of him/her