Yes, you can share code as part of dissertations. Here is an example dissertation that contains a link to a GitHub Repository in the "Related URLs" section: http://d-scholarship.pitt.edu/33801/

This example code package is shared under a CC-BY-NC-SA license, which is labeled on the GitHub repository, but because the student owns the copyright to the created code, they could choose any license for open source software such as a GNU General Public License (have a look at https://choosealicense.com/ for some more information on these licenses).

Using a software and code-specific repository would be the best option, although we could also connect you to our colleagues who can advise on the best ways to package the code to include it alongside his dissertation in the record in D-Scholarship as a downloadable object if that would serve the purpose better.

Please feel free to contact ETD Support  for help with this topic.