I like the idea of only allowing those who submitted rate. But allow anyone to comment.
You can minimise the abuse of creating blank /fake entries by ignoring ratings for users who do not receive a minimum number of rating themselves.
Of course this could be circumvented by creating enough fake accounts to raise each other above the minimum, but again countered by looking for voting islands. Depends how far you want to take the anti cheat measures. There will always be loopholes.
Introducing a Karma system that accounts for participation may help too - this has been discussed in a few other threads.
https://itch.io/t/527869/karma-system-for-the-game-jams
https://itch.io/jam/gmtk-2019/topic/527912/show-some-respect-to-other-participants
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Also, I really hope Mark acknowledges and discusses these rating problems in a video, I'd be keen to understand his perspective as the event organiser.