Like Kathi, I also know of no link between asthma and adhd or autism.  However, as a respiratory therapist, I do give lots of breathing treatments to kids, and I can tell you first hand that it is not uncommon for kids to be unruly during treatments -- in fact, it is quite common.  It can sometimes be a challenge to get them to take their treatments.  Quite often, distractions are the only option -- although challenging.

When your child is on treatments, how often does he take them?  I ask this because one side effect of bronchodilators is they can make kids hyper active.  I see this quite a bit in the hospital.  In fact, I often joke that you know a treatment is working when the kids starts running laps around the bed. 

What bronchodilator do you give your son?  If your doctor prescribed Albuterol, you might want to discuss your doctor prescribing Xopenex, which some studies show has fewer side effects.  The only other option I can think of is to limit the # of treatments you give to only when he is short of breath -- but that may not always be possible with kids.

Keep in mind this is my opinion and personal observation.  Always, the best person to talk with about your concerns is your child's physician.