Adopted with ADHD
My husband has Obsessive ADHD and he is adopted. His parents treated him the same way you would any child with ADHD, adopted or not. When he was really upset he admits that he threw the "you're not my mom/dad" thing in their face, but they never reacted to it so he didn't do it often.
I would say that the best way to discipline a child with ADHD is the same with most kids in the sense that you need to be consistent. The only difference is that you need to understand that the child has a harder time controlling those impulses so try not to get too upset. They still need to learn that the behavior is wrong but it could take several instances of discipline for them to get there. Even then they may slip because ADHD children aren't always in complete control. So I would say the best technique is:
1. Stay calm - never discipline out of anger/frustration
2. Remove the child from the activity/stimulus
3. Ask them to explain what they did wrong (this makes them focus and think through it themselves rather then just tuning you out while you talk)
4. Give them an appropriate consequence and explain why you chose it.
Use the same consequence for that offense everytime. For example: getting to loud/roudy = read a book for 5 minutes and summarize what you read. Hitting sister/brother = sitting in the corner for 5 minutes and the brother/sister gets to pick the next activity. The consistency will help them remember that a certain action equals something they don't like and they'll eventually learn to try and control it.
The obsessive part of his ADHD makes it hard for him to let go of things. Basically the same thoughts loop over and over again in his head - especially negative ones. I've had to learn how to snap him out of it so we can move on with our day.