One difference might be that to get hallucination within a trance one has to do a lot of things (e.g., rituals, dance, music, drugs) to get that far whereas in schizophrenia they come spontaneously and unintended.

  Hallucinations occur in various mental illnesses, in some physical diseases, in fevers, in normals after taking drugs, etc.  I think they are likely to have the same fundamental cause regardless of where they occur.  I doubt that there are any fundamental differences in the form of hallucinations whatever their context, though their interpretation differs widely.

   Are you talking about auditory hallucinations during trances?

Hallusinations alone are naturallly not enough to diagnose schizophrenia. It is like in the two other answers defined by which other symptoms and problems with function the person has.