What are the dangers of using mindfulness-based techniques for individuals suffering from Schizophrenia?
I cannot answer your question, because I'm not an expert on schizophrenia, but I would like to point out that the answer will depend on your theory of schizophrenia.

Post-mortem research on the brains of schizophrenic patients has found consistent anomalies:


widening of the ventricles (meaning a loss of subcortical brain cells)
structural abnormalities in the subcortical temporal-limbic areas such as the hyppocampus and basal ganglia
structural abnormalities in the prefrontal and temporal cortex


CT and MRI research on the brains of living schizophrenics has found similar anomalies:


enlarged ventricles
loss of cortical substance in the temporal and frontal areas
reduced volume in the basal ganglia (nucleus caudatus) and limbic structures


It appears that there is a general atrophy of brain tissue in schizophrenics, and from my non-expert knowledge there is nothing you can do to reverse this. Typical therapy in schizophrenia (today) is to give anti-psychotica to reduce symptoms, behavioral therapy to enhance social abilities, and family therapy to reduce hostility, excessive worrying etc. ("expressed emotion" plays a role in the etiology of schizophrenia). So basically what you do is not "heal" the disorder but alleviate the symptoms and help the patients with their everyday problems.

Since cognitive behavioral therapy (in which the patient is encouraged to consciously deal with his thoughts, including, I'd guess, the paranoic ones) is a normal part of clinical routine with schizophrenia, I don't see why mindfulness could not be beneficial. I believe it might well enhance the CBT in the same way as in the therapy of depression, where mindfulness and CBT are successfully applied in conjunction.