Is there a difference between an organizer and inducer substance?
According to Merriam-Webster they are synonyms:


  [An organizer is]  a region of a developing embryo or a substance produced by such a region that is capable of inducing a specific type of development in undifferentiated tissue —called also inductor


Lifemap and Biology Today support the terms being synonymous as well.

However, I think the most commonly used terminology here is that the organizer [used as a noun] induces [used as a verb] the differentiation of embryonic tissue. For example, consider the following quote (Arizona State University):


  The Spemann-Mangold organizer, also known as the Spemann organizer, is
  a cluster of cells in the developing embryo of an amphibian that
  induces development of the central nervous system