First, Grammarly has nothing to do with this suspension or any problem with the videos in question.
Second, this is not a flaw or a hack but an unsuccessful attempt to use Grammarly for an UNINTENDED purpose. Grammarly is not meant for anti-plagiarism enforcement. Grammarly aims to help users avoid accidental or unintentional plagiarism by highlighting parts that may need to be cited. So it does not attempt to deal with any plagiarisms enforcement countermeasures - if someone is deliberately masking plagiarism, it's definitely not unintentional or accidental. It's trivial to overcome these particular counter-measures but that's just not what Grammarly is for.