Have read a lot lately from people with ADD and ADHD who have a lot of deja vu experiences, and the question is - is it related to the ADD or ADHD? I don't know; I've had a fair number myself and they are very striking.
I did find this post from Dr. Amen, who's doing a lot of cutting edge work with SPECT, a brain imaging technique that I think is still experimental - the link is below. Basically he says that if the SPECT shows abnormalities in the left temporal lobe (could be from head trauma, genetic, or just an aberrant finding), there can be associated deja vu experiences, along with irritability (I have), hallucinations (nope), and other things.
Abnormalities in other areas he connects with other symptoms, including ADD or ADHD related to the frontal cortex.
So the question - is deja vu more common in ADD or ADHD - remains unanswered, grounds for research.
Dr. Amens post clik here