Do IMS journals count as open access?
The definitive place to check is the IMS's Copyright Transfer Agreement, which conclusively says:


  However, the author(s) reserve the following:
  
  
  All proprietary rights other than copyright, such as patent rights.
  The rights to use all or part of this work (with appropriate reference to the journal and article) in future works of
  their own, such as lectures, press releases, reviews, textbooks, or reprint books.
  The right to place the final version of this article (exactly as published in the journal) on their own homepage or in
  a public digital repository, provided there is a link to the official journal site.
  The right to provide a copy of the final peer‐reviewed manuscript to the NIH upon acceptance for publication, for
  public archiving in PubMed Central as soon as possible but no later than 12 months after publication.
  


So the IMS follows the green open access model (which is confirmed by Sherpa/ROMEO).