Hi, my 10 year old daughter also has sensory processing issues in addition to her ADHD.
I would question the diagnosis of ADHD. There are three types of ADHD (predominantly inattentive type, predominantly hyperactive type, and combined type), but what you mention sounds more like sensory problems since it doesn't fit into any of the above--is he so hyper he can't sit still and fidget constantly? While that can be ADHD, it can also be sensory. It's so hard to tell sometimes.
My daughter has a lot of social problems and gets overwhelmed easily. Having more than one neurological 'glitch' complicates things, but I will say that OT and a sensory diet helps a LOT with both the SID and ADHD!
I would just make sure your son gets a very thorough evaluation that includes ruling out other conditions that could look like ADHD.
Good luck with everything. I know how difficult and frustrating it can be to figure out what exactly the problem is!
Maureen