Hope I understood you correctly; not trying to change your mind:
Unless you've already checked w/ other #RDFa parsers, I wouldn't rely on GRRT (referenced blog post). AFAICT, GRRT wasn't parsing the HTML snippet correctly back then nor now for that HTML snippet.
If you don't use the `vocab` attribute, values like `license` are ignored by the RDFa parser (unless host language's default vocab is applied). For anything else parsing plain ol' rel=license, that's not an issue anyway.