video could absolutely prove a lot with no audio. If they shake hands and she walks away with a smile on her face... that doesnt exactly look like someone who was just offended by some comments. Now if they are smiling and all of the sudden her facial expression changes from smiles to one of outrage or shock in an instant, that would back up her claim. If she is smiling the entire time and then smiling as they part from each other, that backs up mike. AND, the video will show how close those 3 men that stepped up on Mike;'s behalf were to the incident. Were they right there and could easily hear the conversation? If so, and they say nothing happened, the video backs them up.
BUT, why would Marriott be resisting releasing the video? If it helped them, you can be damn sure they would have already turned that video over.