There are several other excellent online guides to using copyrighted materials in your dissertation, and considering post-publication issues such as the value of publishing open access and when to choose an embargo.
University of Michigan's Copyright for Dissertations: Getting Started
University of Michigan's A Graduate Student's Guide to Copyright: Open Access, Fair Use, and Permissions (from 2010)
Hillary Corbett, ETDs and the Consequences of Openness
Ohio State's Copyright in Your Thesis or Dissertation
If your particular question isn't addressed here, there's a good chance that U.S. Copyright Office's Compendium has something to say about whether that type of resource is copyrightable, and the level of protection it receives.