The results of the twins studies also applies to mental illnesses such as schizoprenia, which could hardly be said to be an adaptive outcome of genetics. I'd hazard to guess that even those cases where genetics plays a large part the outcome is still an anomalyThere's a school of thought these days that schizophrenia is a byproduct of the evolution of human intelligence. So yes, schizophrenia could be an adaptive outcome.
Actually, schizophrenia is maladaptive, not adaptive. Adaptive outcomes have benefits.