The file `dictionary` used by `passgen` is a slightly modified form of the wordlist found at:
https://www.wordgamedictionary.com/sowpods/download/sowpods.txt

The same exact list of words can be found in the following git repository under the MIT license:
https://github.com/jesstess/Scrabble

Thus I conclude it is safe to include this list in a BSD licensed repository.