Operant conditioning relies on the subject initiating an action that is followed by some consequence. The DMS-IV defines abnormal behavior to include anxiety disorders, affective disorders (i.e. depression), obsessive-compulsive disorders, schizophrenic disorders and personality disorders. Many of these disorders result from chemical imbalances or organic issues within the brain. Using operant conditioning as a treatment would only make since if it was a small part in the larger picture of treatment which should include medication and other types of therapy. Operant conditioning has been used with some effectiveness in treatment of obsessive-compulsive behaviors as well as anxiety disorders, phobias, and separation anxiety.
I dont think a consequence cuts it correctly, it is more incentive or didsincentive. A consequence could be benign, if I do well in work I get praise, or more money is incentive, if I do well in work and a flowerpot falls off the window ledge --how does that affect me?
Also the question is not clear, behavioural theapy is useful for some disorders, but OC can also be seen to facilitate and develop abnormal behaviour, which I see as the premis of the question. If some one behaves in a certain way and gets a reward they may continue to do it. Such as secondary gains for sick people. If your sick people care for you, cook, get things, spend time with you etc stay sick get looked after.
Chemical imbalances, could be chicken and egg, there are different patterns for chemicals in the brain when certain disorders are evident but the evidence is correlational and for some conditions, weak.