Visual spatial weaknesses would be assessed by the combination of an occupational therapist and psychologist (neuro, school, or clinical). His relative weaknesses in this area are already documented in your existing assessments, but might be further clarified in additional testing. Since he has already been seen by an OT, without any significant findings, I would probably wait on this until the active/inattentive behavior has been figured out a bit more.
Auditory processing would have very little to do with visual spatial skills, but might be a possible avenue for investigation with respect to apparent attention problems, as the two often have similar symptoms. The professional who assesses this area is an audiologist; you may be able to obtain a referral for this through your health insurance/primary care provider.
Regarding ADHD: an OT is not really the professional with the appropriate training for ruling this out. For this, you would want a child psychiatrist, psychologist, or neurologist.
