I put some effort into researching the law that might be applied to religious teaching that causes terrorism.  There is a theory of jurisprudence around the concept of a "true threat."  Presumably if a true threat were issued by a religious leader in a religious setting there is a body of precedent that that might be used to evaluate that that threat.  Unfortunately, the precedents do not at this time provide clarity.  They are a "muddled mess" to quote this article reviewing the area:
http://www.firstamendmentcenter.org/true-threats

Obviously we now have many cases where religious leadership has yielded the joining of ISIS or funding their operations.  Such actual direct actions or substantive support for such actions that would lend much credibility to murderous religious pronouncements being an actual "true threat."  However, it seems that we would need any law in this are to be more clearly drawn so that a judge or jury would not have to make sense of what is now said to be a muddled mess.

Don