Right now, you can find the "Rate for GameMaker 20 Jam #GM20" link on the game's actual "game page" --- not the GM20 Jam's game "submission" page. (I hope that's clear enough. That was hard to explain.)
Yes, but if you follow that link, there is no way to rate the game. (That page IS the same page reached from the submission page.)
There should be a rating section between the post and comment sections on that page.