Basically ADHD is just a symptom checklist, what causes it also causes a whole variety of other stuff not included in the same checklist for somewhat @political" reasons.
In particular ODD means being reflexively and exaggeratedly defiant and hostile to authority. Possibly because its associated with external demands that are inherently difficult to meet (because of the ADHD part) and so quite tortuous and frustrating.
What's remarkable is that the oppositional characteriststs associated wiith ADHD are significantly helped by stimulants. Which doesnt make any sense, if the oppositionality were some personality characteristic. It arises due to the very same cognative impairments.
I have ADHD. I tend to notice that other people I know, who also have ADHD, tend to have a lot of other "not normally associated with ADHD" things in common with me. But I don't know which are true correlations, and which are just pareidolia on my part.
Chalking it up to dopamine is a gross simplification.
Adderal, for example, stimulates the release / reduces the re-uptake of dopamine, norepinephrine, epinephrine, serotonin, histamine, and CART peptides.